This is a follow-on to comments in https://review.openstack.org/156356
and https://review.openstack.org/#/c/151513/
* Remove work-around for /var/cache/pip
* Remove WHEELHOUSE setting in tools/build_wheels.sh and use the pip
default directory '<cwd>/wheelhouse'
* Remove bogus MySQL-python install
* Removed unused bits and clean up pip commands in from tools/build_venvs.sh
Closes-Bug: #1423720
Change-Id: I0283b0dff9146b1b63bd821358505a93566270c6
Introduce the tooling to build virtual environments.
* tools/build_venv.sh: build a venv
* introduce lib/stack to house functionality extracted from stack.sh that
is needed in other places, such as Grenade; start with stack_install_service
to wrap the venv install mechanics
* declare PROJECT_VENV array to track where project venvs should be installed
* create a venv for each project defined in PROJECT_VENV in stack_install_service()
Change-Id: I508588c0e2541b976dd94569d44b61dd2c35c01c