MB-8858: additional wait ep_warmup_thread=complete

to be sure that warmup completed.

Change-Id: I780834d22dcac9035d0a1a57b691b6c768a6160e
Reviewed-on: http://review.couchbase.org/28310
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>