MB-5307: implemented faster bucket config access
MB-5307: implemented faster bucket config access

Apparently sending config out of ns_config process is becoming a
performance problem. get_bucket call even for 4 nodes without notable
vbucket map history and with just one bucket takes around 200
microseconds.

This commit speeds up get_bucket/1 call by doing searching on
ns_config process and thus by avoiding sending out entire ns_config
state. There's also even lighter get_bucket_light/1 call which strips
vbucket map from reply making copying even less expensive.

Change-Id: Ib54ced6993c12640566f68be0876030727c400ad
Reviewed-on: http://review.couchbase.org/17752
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

ceejatec/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,daverigby/ns_server,vzasade/ns_server,daverigby/ns_server,nimishzynga/ns_server,ceejatec/ns_server,nimishzynga/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,nimishzynga/ns_server,vzasade/ns_server,pavel-blagodov/ns_server,daverigby/ns_server,vzasade/ns_server,membase/ns_server,vzasade/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,daverigby/ns_server,daverigby/ns_server,nimishzynga/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,pavel-blagodov/ns_server,nimishzynga/ns_server,ceejatec/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,t3rm1n4l/ns_server,membase/ns_server,mschoch/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server