LU-6013 util: test harness use mount.lustre_osd

Allow the test harness to use mount.lustre_osd by bind
mounting /sbin/mount.lustre_osd to the in-tree copy, as is
already done for mount.lustre

Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Change-Id: I4c18e972f2ca09ed4aab949611d5d67e4ec7943e