LU-288 adjust PATH order in test framework

LU-288 adjust PATH order in test framework

* Test scripts use lustre build tree binaries other than installed ones.
* Bind mount mount.lustre in the lustre build tree other than copying to /sbin/

Change-Id: I32468fa608b32a7ef097db531cdd45b68088af50
Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/525
Tested-by: Hudson
Reviewed-by: Lai Siyao <laisiyao@whamcloud.com>
Reviewed-by: Prakash Surya <surya1@llnl.gov>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>