Fix for bug 637936: killing both redundant logs causes deadlock

Fix for bug 637936: killing both redundant logs causes deadlock

Problem:
When both legs of a mirrored log fail, neither the log nor the parent
mirror can proceed.  The repair code must be careful to replace the
log with an error target before operating on the parent - otherwise,
the parent can get stuck trying to suspend because it can't push through
any writes.  The steps to replace the log device with an error target
were incomplete and resulted in the replacement not happening at all!

The code originally had all the necessary logic to complete the
replacement task, but was pulled out in a effort to clean-up that
section of code, while fixing another bug:
<offending commit msg>
In addition, I added following three changes.

- Removed tmp_orphan_lvs handling procedure
  It seems that _delete_lv() can handle detached_log_lv properly
  without adding mirror legs in mirrored log to tmp_orphan_lvs.
  Therefore, I removed the procedure.

- Removed vg_write()/vg_commit()
  Metadata is saved by vg_write()/vg_commit() just after detached_log_lv
  is handled. Therefore, I removed vg_write()/vg_commit().
</offending commit msg>

http://sources.redhat.com/cgi-bin/cvsweb.cgi/LVM2/lib/metadata/mirror.c?cvsroot=lvm2&f=h#rev1.130

I've reverted the "clean-up" changes associated with that fix, but not what
that commit was actually fixing.

Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Reviewed-by: Petr Rockai <prockai@redhat.com>