LU-5573 obdclass: strengthen against concurrent server mounts

LU-5573 obdclass: strengthen against concurrent server mounts

This patch is an add-on to previous fix for LU-5299, against same
issues/races scenarios during concurrent server devices mounts.

This patch is back-ported from the following one:
Lustre-commit: 91b68bc4f4d8f25e88a252ca0918f0a422fec27b
Lustre-change: http://review.whamcloud.com/12114

Test-Parameters: alwaysuploadlogs \
envdefinitions=SLOW=yes,ENABLE_QUOTA=yes,CONF_SANITY_EXCEPT=45 \
mdtfilesystemtype=zfs mdsfilesystemtype=zfs ostfilesystemtype=zfs \
ostcount=2 ostsizegb=8 testlist=conf-sanity,conf-sanity,conf-sanity

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: I121ee3f14d4bee7973cd968d561e8fc03acb6386
Reviewed-on: http://review.whamcloud.com/12353
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>