This was originally required to allow other methods in SourcesList to
fail, but subsequent changes rendered that unnecessary, and it's just
a cleanup now, and avoids passing in module separately to save().
1. Don't test check_mode in both the caller and in the callee.
2. Don't test HAVE_PYTHON_APT inside an if that tests HAVE_PYTHON_APT
3. Don't be irritatingly vague about why the module fails ("You may be
seeing this because…").
Note that if «apt-get -y install python-apt» succeeds with rc==0, but
for some reason python_apt is not usable afterwards, this will break
because the imports in install_python_apt aren't wrapped inside a
try/except.
In other words, we assume that install_python_apt either succeeds or
fails with a traceback. This commit doesn't affect that behaviour.
The original problem is: apt_repository.py connect to launchpad on
every playbook run. In this patch apt_repository.py checks if required
repository already exists or not. If no - paa will be added, if yes -
just skip actions.
