gfs2: Don't write log headers after file system withdraw

gfs2: Don't write log headers after file system withdraw

Before this patch, when a node withdrew a gfs2 file system, it
wrote a (clean) unmount log header. That's wrong. You don't want
to write anything to the journal once you're withdrawn because
that's acknowledging that the transaction is complete and the
journal is in good shape, neither of which may be a valid
assumption when the file system is withdrawn. This is especially
true if the withdraw was caused due to io errors writing to the
journal in the first place. The best course of action is to leave
the journal "as is" until it may be safely replayed during
journal recovery, regardless of whether it's done by this node or
another.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>