MB-100: bump ns_server:get timeout

Because sometimes xdcr and views could be abused to such extent that
even prioritized ns_config may have issues serving requests quickly
enough.

Change-Id: Ife261ce77bd80b6e815343b30a239ed7c54fd2a2
Reviewed-on: http://review.couchbase.org/27584
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>