LU-2729 mgs: fix cleanup of nonexistant MGSSELF_NAME proc file

LU-2729 mgs: fix cleanup of nonexistant MGSSELF_NAME proc file

The mgs teardown code gets invoked in the failure case but assumes
that the MGSSELF_NAME proc file has been created. If it hasn't been
created, the proc code issues a WARN_ON.

The setup code clears the FSDB_MGS_SELF from &fsdb->fsdb_flags when it
creates the proc file, so we can key off of that to decide whether to
remove it.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Change-Id: Idf58d1fa572eeced5dbaa72f03e38ee46a708166
Reviewed-on: http://review.whamcloud.com/5122
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>