Allow per node config requests return global values.
Allow per node config requests return global values.

In case '_use_global_value' atom corresponds to some key or subkey in
a config then global value will be returned by search_node and
search_node_prop functions.

Change-Id: Ic815c7658d113e9ebef746e56ad3d1db24e32a47
Reviewed-on: http://review.couchbase.org/9155
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

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