check_lock: treat 'locked by other' differently to 'not locked'

check_lock currently claims the daemon is locked by another app
even if the problem is actually that it *isn't locked at all*.
We should distinguish these two cases.

Also, here and in a few other places we refer to this as either
a 'dnf lock' or a 'yum lock'. AFAICT it is not either of those
things, it is a lock that is internal to the daemon. You can
happily perform operations with dnf *directly* while this lock
is held. It's confusing to describe this as a 'dnf lock' when
that isn't what it is, so this changes the description to
'dnfdaemon lock' in a few places.

Signed-off-by: Adam Williamson <awilliam@redhat.com>