With ansible 2.2, apt_repository update_cache feature has
been fixed. When a new repo will be added, apt-get update
will be run after the addition if update_cache is set to yes.
This combined with the apt module now properly checking the
cache validity, we can now have proper updating of the cache
with registering variables.
Change-Id: I70a9892f11c754aba44a7a6e0d99cec515ba3e33