LU-7803 tests: Cleanup after sanity/78

LU-7803 tests: Cleanup after sanity/78

Remove large file created by sanity/78 regardless of failure.  If this
file is left after failure, it causes some cascading failures because
of limited space available.

Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: Ib359b9024360015ce92f209e5350f2d679071cb8
Reviewed-on: http://review.whamcloud.com/21808
Tested-by: Jenkins
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>