Imports to fix build warnings

There were warnings generated during the build due to missing
attributes, like this:

 keystoneclient.rst:7: WARNING: missing attribute mentioned in
   :members: or __all__: module keystoneclient.__init__, attribute
   v2_0

This is fixed by importing the symbol in __init__.

Closes-Bug: #1315523

Change-Id: I565c78ef8910353c4e1ce1641b42fba7cdbd77d8
Doc build fails if warnings

If the docstrings are invalid then the commit should fail the gate.

Change-Id: Iabe506fa914ac5e742c0c5f4682ed0471c4a64ca
Merge "Imports to fix build warnings"
Merge "Doc build fails if warnings"