CBQE-2108 Extend wait for warmup to avoid temporary errors from Memcached

Change-Id: Ie0001d9fa6e02320a5380ff8d7634e5f310b0fcc
Reviewed-on: http://review.couchbase.org/35196
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Reviewed-by: Aruna Piravi <aruna@couchbase.com>
Tested-by: Aruna Piravi <aruna@couchbase.com>