Update apt_repository to query if repo is already configured

This adds two dependencies to the apt_repository module:  apt and
apt_pkg.  These come from the package python-apt.  This is used to parse
the host's sources.list and examine whether the repo is already
configured.  This then eliminates the unnecessary
'add-apt-repository --remove' from running.
Merge pull request #1907 from sfromm/issue1888

Update apt_repository to query if repo is already configured