CBQE-1012: kill old processes for ui job

Change-Id: I3d2ef1aca40fded88a1c644248985b543cc29344
Reviewed-on: http://review.couchbase.org/25537
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: buildbot <build@couchbase.com>