LU-10443 test: Handle file lifecycle correctly

LU-10443 test: Handle file lifecycle correctly

The current lockahead_test.c removes the test file on exit,
which will destroy the locks which sanity.sh counts to
verify correct operation.  This usually works because
sanity.sh wins the race with the object destroy command
from the MDS to the OSS.

Change lockahead_test.c to remove the test file on entry,
and to use $tfile rather than its own file, so it is
automatically cleaned up by sanity.

Change-Id: I3cd1fdb7f33da167ca21476a7b3cbe5f57fd5782
Signed-off-by: Patrick Farrell <paf@cray.com>
Reviewed-on: https://review.whamcloud.com/31254
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Wei Liu <wei3.liu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>