MB-100: less logs when waiting is_ns_server_running

Change-Id: Ib962fe0a0cd41ae951ee5eb072ff1a82ba86fc42
Reviewed-on: http://review.couchbase.org/23652
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: buildbot <build@couchbase.com>