Add 3 new environment variables during gate-check-commit and
bootstrap-ansible which allow for skipping the ansible-runtime venv
build, the bootstrap-aio role execution, and the OSA role clone.
Any value set to the skip variables will cause the execution of
that item to skip.
The environment variables added are:
SKIP_OSA_RUNTIME_VENV_BUILD
SKIP_OSA_BOOTSTRAP_AIO
SKIP_OSA_ROLE_CLONE
These will be used to skip the steps in the gate as we will shift
to running these in the Zuul pre-run phase. They can be run multiple
times, but skipping them will decrease execution time.
Change-Id: I96d73cf196fb4ede8ec163cac2971a45c757106f