LU-1538 tests: unmount /sbin/mount.lustre bind mount

LU-1538 tests: unmount /sbin/mount.lustre bind mount

If the lustre/utils/mount.lustre file has changed since it was bind
mounted on /sbin/mount.lustre, unmount it and mount the new one
there, to avoid strange problems when testing from a local tree

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: Ie5360dae9f33553acb914c8ce549e848c1500c1e
Reviewed-on: http://review.whamcloud.com/8912
Tested-by: Jenkins
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>