Enable CLI JSON output for script consumption

[kevin-bates]

This change allows for elyra-metadata list <namespace> --json output to be piped to JSON-aware tools for consumption. It allows for usage w/ and w/o the --valid-only flag where invalid entries will have a reason with a value entry.

Errors still appear on stderr but stdout can be piped or redirected.

Resolves #742

Here are some outputs after piping to jq...

With --valid-only...

$ elyra-metadata list runtimes --json --valid-only |jq
[E 2020-07-09 17:03:36,372.372] JSON failed to load for metadata 'foo' in namespace 'runtimes' with error: Expecting ',' delimiter: line 10 column 5 (char 318).
[E 2020-07-09 17:03:36,377.377] Schema validation failed for metadata 'foofoo' in namespace 'runtimes' with error: None is not of type 'string'.
[E 2020-07-09 17:03:36,379.379] Schema validation failed for metadata 'barbar' in namespace 'runtimes' with error: 'xxx' is too short.
[
  {
    "name": "foodoo",
    "display_name": "Foo Doo",
    "metadata": {
      "api_endpoint": "http://wackwach",
      "cos_endpoint": "http://zackzach",
      "cos_username": "cos_username",
      "cos_password": "cos_secret",
      "cos_bucket": "cos-chuckit"
    },
    "schema_name": "kfp",
    "resource": "/Users/kbates/Library/Jupyter/metadata/runtimes/foodoo.json"
  },
  {
    "name": "baz",
    "display_name": "BAZ",
    "metadata": {
      "api_endpoint": "http://codait.org",
      "cos_endpoint": "http://baz.boo",
      "cos_username": "charles",
      "cos_password": "farles64",
      "cos_bucket": "chuckit"
    },
    "schema_name": "kfp",
    "resource": "/Users/kbates/Library/Jupyter/metadata/runtimes/baz.json"
  },
  {
    "name": "kf_1",
    "display_name": "KubeFlow 1.0",
    "metadata": {
      "api_endpoint": "http://cloning1.fyre.ibm.com:31380/pipeline",
      "cos_endpoint": "http://cloning1.fyre.ibm.com:31671",
      "cos_username": "minio",
      "cos_password": "minio123",
      "cos_bucket": "kbates"
    },
    "schema_name": "kfp",
    "resource": "/Users/kbates/Library/Jupyter/metadata/runtimes/kf_1.json"
  }
]

Without --valid-only so invalid entries are included...

$ elyra-metadata list runtimes --json |jq
[E 2020-07-09 17:04:35,389.389] JSON failed to load for metadata 'foo' in namespace 'runtimes' with error: Expecting ',' delimiter: line 10 column 5 (char 318).
[E 2020-07-09 17:04:35,394.394] Schema validation failed for metadata 'foofoo' in namespace 'runtimes' with error: None is not of type 'string'.
[E 2020-07-09 17:04:35,395.395] Schema validation failed for metadata 'barbar' in namespace 'runtimes' with error: 'xxx' is too short.
[
  {
    "name": "foodoo",
    "display_name": "Foo Doo",
    "metadata": {
      "api_endpoint": "http://wackwach",
      "cos_endpoint": "http://zackzach",
      "cos_username": "cos_username",
      "cos_password": "cos_secret",
      "cos_bucket": "cos-chuckit"
    },
    "schema_name": "kfp",
    "resource": "/Users/kbates/Library/Jupyter/metadata/runtimes/foodoo.json"
  },
  {
    "name": "baz",
    "display_name": "BAZ",
    "metadata": {
      "api_endpoint": "http://codait.org",
      "cos_endpoint": "http://baz.boo",
      "cos_username": "charles",
      "cos_password": "farles64",
      "cos_bucket": "chuckit"
    },
    "schema_name": "kfp",
    "resource": "/Users/kbates/Library/Jupyter/metadata/runtimes/baz.json"
  },
  {
    "name": "kf_1",
    "display_name": "KubeFlow 1.0",
    "metadata": {
      "api_endpoint": "http://cloning1.fyre.ibm.com:31380/pipeline",
      "cos_endpoint": "http://cloning1.fyre.ibm.com:31671",
      "cos_username": "minio",
      "cos_password": "minio123",
      "cos_bucket": "kbates"
    },
    "schema_name": "kfp",
    "resource": "/Users/kbates/Library/Jupyter/metadata/runtimes/kf_1.json"
  },
  {
    "name": "foofoo",
    "display_name": "Foo Baz",
    "metadata": {
      "description": null,
      "api_endpoint": "http://wackwach",
      "cos_endpoint": "http://zackzach",
      "cos_username": "cos_username",
      "cos_password": "cos_password",
      "cos_bucket": "cos_chuckit"
    },
    "schema_name": "kfp",
    "resource": "/Users/kbates/Library/Jupyter/metadata/runtimes/foofoo.json",
    "reason": "ValidationError"
  },
  {
    "name": "barbar",
    "display_name": "KFP with IBM COS (yukked1)",
    "metadata": {
      "api_endpoint": "http://yukked1.fyre.ibm.com:31380/pipeline",
      "cos_endpoint": "https://s3.us-south.cloud-object-storage.appdomain.cloud",
      "cos_username": "xxx",
      "cos_password": "xxx",
      "cod_secure": "True",
      "cos_bucket": "xxx"
    },
    "schema_name": "kfp",
    "resource": "/Users/kbates/Library/Jupyter/metadata/runtimes/barbar.json",
    "reason": "ValidationError"
  },
  {
    "name": "foo",
    "display_name": null,
    "metadata": {},
    "schema_name": "{unknown}",
    "resource": "/Users/kbates/Library/Jupyter/metadata/runtimes/foo.json",
    "reason": "ValueError"
  }
]

And when no pipe/redirection is used...

$ elyra-metadata list runtimes --json --valid-only 
[E 2020-07-09 17:04:12,716.716] JSON failed to load for metadata 'foo' in namespace 'runtimes' with error: Expecting ',' delimiter: line 10 column 5 (char 318).
[E 2020-07-09 17:04:12,722.722] Schema validation failed for metadata 'foofoo' in namespace 'runtimes' with error: None is not of type 'string'.
[E 2020-07-09 17:04:12,723.723] Schema validation failed for metadata 'barbar' in namespace 'runtimes' with error: 'xxx' is too short.
[{
  "name": "foodoo",
  "display_name": "Foo Doo",
  "metadata": {
    "api_endpoint": "http://wackwach",
    "cos_endpoint": "http://zackzach",
    "cos_username": "cos_username",
    "cos_password": "cos_secret",
    "cos_bucket": "cos-chuckit"
  },
  "schema_name": "kfp",
  "resource": "/Users/kbates/Library/Jupyter/metadata/runtimes/foodoo.json"
}, {
  "name": "baz",
  "display_name": "BAZ",
  "metadata": {
    "api_endpoint": "http://codait.org",
    "cos_endpoint": "http://baz.boo",
    "cos_username": "charles",
    "cos_password": "farles64",
    "cos_bucket": "chuckit"
  },
  "schema_name": "kfp",
  "resource": "/Users/kbates/Library/Jupyter/metadata/runtimes/baz.json"
}, {
  "name": "kf_1",
  "display_name": "KubeFlow 1.0",
  "metadata": {
    "api_endpoint": "http://cloning1.fyre.ibm.com:31380/pipeline",
    "cos_endpoint": "http://cloning1.fyre.ibm.com:31671",
    "cos_username": "minio",
    "cos_password": "minio123",
    "cos_bucket": "kbates"
  },
  "schema_name": "kfp",
  "resource": "/Users/kbates/Library/Jupyter/metadata/runtimes/kf_1.json"
}]

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