LU-8295 tests: comply with OBD_RACE() behavior

LU-8295 tests: comply with OBD_RACE() behavior

Have conf-sanity/test_41c better comply with OBD_RACE() internal
behavior when creating a racy situation with 2 similar mount
cmds being run in parallel.

CFS_FAIL_ONCE must be set, and fail_loc must only be reset when
it is sure that both mount commands have reached the race
rendez-vous, in order to have OBD_RACE() behave as expected.

start() function is no longer used to avoid extra tools which
surround mount command to interfer due to concurrency.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: Ic513c82c4fd1395d88144cf1c590a08dfd3c11e5
Reviewed-on: https://review.whamcloud.com/21117
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>