Remove plugin pip-requires.

Remove plugin pip-requires.

Fixes bug 906636.

The cisco plugin included ncclient, but does not use it when testing.
The openvswitch plugin included SQLAlchemy which is already required
by quantum itself.

I've also changed the install_venv.py script to only look at
tools/pip-requires, so that it behaves more like the rest of the
OpenStack projects.  In Jenkins that's the only file we look at
to see if we need to rebuild the virtualenv, so it would be best
if the project only hade one pip-requires.

Also added .gitignore to ignore files created during testing.

Change-Id: Ic460452ec89aa8377c975ca63b57563119860e6b