Fix importing config module and classmethod params

The Token/Endpoint options specify an instance method where the
expectation is a classmethod. This prevents the class being loaded from
config file or CLI.

The cfg module was not imported so loading plugins would raise an
AttributeError.

Change-Id: I33b4a8c181210d74d4779438afc1f918e06df85b
Merge "Fix importing config module and classmethod params"
Correct Session docstring

The online docs for the Session class are unusable because the
arguments to __init__ were not displayed.

This and other issues in the docstrings for the class are corrected.

Change-Id: Ia03b785f132f7d21ba576c0c8d634051d7127319
Correct documenting constructor parameters

When the docs are rendered to HTML, any docs on __init__ are not
displayed. The parameters to the constructor have to be documented on
the class rather than on the __init__ method.

Also, corrected other minor issues in the same areas.

Change-Id: Ic56da33f6b99fe5efb636c289e3c4e1569f0c84c
Pass all adapter parameters through to adapter

We can't simply pass through kwargs to the adapter for compatibility
reasons however make sure that we accept the appropriate arguments and
pass them to adapter.

Also add some notes to try and keep them up to date.

Closes-Bug: #1399492
Change-Id: If72295590483bb52fcf5a0d59cf95f3e49ea69c8