MB-8547:  use "rm -f" in case the files don't already exist

Change-Id: I7688e57e1f97238cb4f5154f13ed283af9e6c83d
Reviewed-on: http://review.couchbase.org/27271
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>