LU-1685 test: fix FAIL_ON_ERROR=false parameter

LU-1685 test: fix FAIL_ON_ERROR=false parameter

The previous fix on LU-1528 which was supposed to
fix the overall status to FAIL when a subtest FAIL
didn't work. This commit will provide the proper
fix. The issue is grep FAIL: in exit_status() should
not include ":"

Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Change-Id: I7eaf14351ac8a2c3d21f530e43c75871b4b01f6a
Reviewed-on: http://review.whamcloud.com/3507
Tested-by: Hudson
Reviewed-by: Yu Jian <yujian@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Cliff White <cliffw@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>