apt_repository: fix update cache after state=changed. Closes GH-4136
apt_repository: added option update_cache.

The default behavior is to update_cache if changed.

If you add more then one repo, you may not want to update cache for every repo separately.
So you can now disable update_cache with this new option e.g. update_cache=no

Updating cache can also be handled using the apt module.
Merge branch 'fix/apt_repository_update_cache' of https://github.com/resmo/ansible into resmo-fix/apt_repository_update_cache