The new aa-enabled program can be used as a barebones replacement for
`aa-status --enabled`. It is written in C, rather than Python, which
keeps its dependencies to a minimum.

By default, aa-enabled prints a human-readable status of AppArmor's
availability to stdout. It supports a --quiet option which allows for
functionality equivalent to `aa-status --enabled`, which does not print
any messages.

The aa-enabled exit statuses mimic the behavior documented in the
aa-status(8) man page.

Signed-off-by: John Johansen <john.johansen@canonical.com>
[tyhicks: Incorporated feedback from the code review process]
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>