Fixes #7696

printf-related TypeError.

Fixes #7414

If we try to use the user module without being root, it fail on RHEL/Fedora
because usermod --help cannot be run. The root cause is lack of permission
due to EAL4+ certification, as seen in shadow-utils changelo.

So if we cannot run it, assume there is no append. It doesn't matter
much since we will not be able to run usermod at all with or without the
option.

Signed-off-by: Chris Lamb <chris@chris-lamb.co.uk>

While migrating my playbook to a newer ansible version, I faced
the error message "unknown init system, cannot enable service". It turned
out to be caused by a wrong service name that was not expanded anymore.

So by giving the name of the service that cannot be enabled and a more precise
reason, i think people will be able to diagnose their issue more easily.

Both 'default' and 'choices' options were missing at the documentation.

Fixes #6911

from mpdehaan and redone entirely.

When no vg_options are passed to the module, 'vg_options' still exists
in the module.params dict with a value of None, so the default empty string in
the get method is never used. None cannot be "splitted", which backtraced.

Fixes #6806

Also adds an integration test for authorized_key for future validation.

Fixes #6700