xfs_repair and xfs_db both check for a dirty log, using roughly
the same cut and pasted code.
Add a new helper to do this, xlog_is_dirty(), and use it instead.
Note, the helper (and the code before it) is a little odd in that
it (re-)initializes some libxfs_init_t members before proceeding,
I haven't yet worked out if that's necessary or correct, so I've
just kept the same behavior for now. Still, it seems like this
should be done in libxfs_init, or not at all.
Signed-off-by: Eric Sandeen <sandeen@redhat.com> Reviewed-by: Brian Foster <bfoster@redhat.com> Signed-off-by: Dave Chinner <david@fromorbit.com>