Sync latest install_venv_common from oslo.

This commit syncs the latest install_venv_common from oslo which
fixes an issue with importing from tempest.openstack.common. This
is needed to run tools/install_venv.py in a non-devstack environment.

Change-Id: I37812c9e0cd432a05ef63eba38fb91ea6df98a0b
Merge "Sync latest install_venv_common from oslo."