CBQE-0: 95% du in test_restart_node_with_full_disk

Change-Id: Ibc594f1450b266558fbe0dfe35e56acac04467c7
Reviewed-on: http://review.couchbase.org/26903
Reviewed-by: Chisheng Hong <chisheng@couchbase.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>