qlit: Tighten QLit list vs QList comparison

We check that all members of the QLit list are also in the QList.  We
neglect to check the other direction.  Fix that.

While there, use QLIST_FOREACH_ENTRY() to simplify the code and break
the loop on the first mismatch.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20170825105913.4060-13-marcandre.lureau@redhat.com>
[Commit message improved]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
