Update our docstrings for PEP 257

[daspecster]

PyLint has added checks to more closely follow PEP 257 which caused linting to fail. We should update our docstrings so we can revert #1967.

[tseaver]

Note that pylint 1.6 actually barfs on two of our source files:

• gcloud/bigtable/happybase/connection.py
• gcloud/streaming/http_wrapper.py

[tseaver]

See: pylint-dev/pylint#998

[dhermes]

I'm digging in to this (hopefully the global disables in #1974 can be addressed easily)

[dhermes]

I commented on pylint-dev/pylint#125, which flags our use of grpc.framework.interfaces.face.face.NetworkError with

Catching an exception which doesn't inherit from BaseException: NetworkError (catching-non-exception)

[tseaver]

Via #1996.