libdevmapper prints garbage on shutdown

libdevmapper prints garbage on shutdown

This patch fixes 2 logging bugs:
  o multipath command prints unexpected log message like
    "libdevmapper: libdm-common.c(303): Created /dev/mapper/<mapname>"
  o multipathd doesn't log messages like "--------shut down------"
    during the exit path

What is the problem:
  o multipath command and multipathd register dm_write_log() using
    dm_log_init() and it can be called from libdevmapper codes like
    dm_lib_release().
  o dm_write_log() references the global "conf" to find the verbosity,
    but it is freed before dm_lib_release() calls dm_write_log().
  o So dm_write_log() reads garbage value like big vervosity.

What does the patch do:
  o multipath command sets NULL to "conf" after freeing it.
    This prevents dm_write_log() from reading garbage data.
  o multipath command and multipathd free "conf" after all logging
    are completed, because the logging functions reference it
    to find the verbosity.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>