Make 'cover' job use always venv
Make 'cover' job use always venv

Without this change 'cover'job starts dialog for running
either in host env or venv and fails not getting proper choice.

Therefore, make it use venv always.

Change-Id: I411ac40a1fde61cbeb725cf5dba850ab6a82e95c

openstack/manila-ui,openstack/manila-ui,openstack/manila-ui