LU-4066 test: use $LUSTRE to locate server modules

LU-4066 test: use $LUSTRE to locate server modules

In test-framework.sh's init_test_env look for $LUSTRE/mdt/mdt.ko
rather than `$dirname $0`/../mdt/mdt.ko to determine if the server
modules are present when they cannot be found in /lib/modules.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Ib16eee4d7811afcb310c7b0fd4a401ea5af2e7ad
Reviewed-on: http://review.whamcloud.com/7854
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>