CBQE-2290: fix warmup progress tests

Change-Id: Icbca334901461dc79e9794c834b0bf8dab1b51b5
Reviewed-on: http://review.couchbase.org/38932
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>