mlaunch: Use default SASL/SCRAM mechanisms when creating users.

[matthewdale]

Description of changes

There is currently a check that explicitly prevents creating a SCRAM-SHA-256 user credential for newer server versions. Remove that SASL/SCRAM default mechanism override now that all official MongoDB drivers support SASL/SCRAM mechanism SCRAM-SHA-256 (see DRIVERS-439).

Fixes #879

Testing

1. Create a standalone deployment with auth enabled.

python3 mtools/mlaunch/mlaunch.py init \
    --dir ~/data/mtools/5.0.0 \
    --single \
    --binarypath $(m bin 5.0.0)  \
    --auth

2. List user info and confirm that credentials for all default SASL/SCRAM mechanisms for MongoDB v5.0.0 are created (SCRAM-SHA-1, SCRAM-SHA-256).

mongosh "mongodb://user:password@localhost:27017/admin" --quiet --eval "db.system.users.find()"
[
  {
    _id: 'admin.user',
    userId: UUID("72e25aa8-a058-47a4-b83b-d7c856291511"),
    user: 'user',
    db: 'admin',
    credentials: {
      'SCRAM-SHA-1': {
        iterationCount: 10000,
        salt: <REDACTED>,
        storedKey: <REDACTED>,
        serverKey: <REDACTED>
      },
      'SCRAM-SHA-256': {
        iterationCount: 15000,
        salt: <REDACTED>,
        storedKey: <REDACTED>,
        serverKey: <REDACTED>
      }
    },
    roles: [
      { role: 'dbAdminAnyDatabase', db: 'admin' },
      { role: 'readWriteAnyDatabase', db: 'admin' },
      { role: 'userAdminAnyDatabase', db: 'admin' },
      { role: 'clusterAdmin', db: 'admin' }
    ]
  }
]

O/S testing:

O/S	Version(s)
Linux
macOS	12.4
Windows

[stennie]

Thanks @matthewdale !