[bp] Link parent instead of monitoring in ns_pubsub.
[bp] Link parent instead of monitoring in ns_pubsub.

This ensures that if handler dies for some reason then parent will die
as well.

Originally reviewed on http://review.couchbase.org/13583

Change-Id: Ide8bdf300c3846f5c7128c2f955f658ad820bc5b
Reviewed-on: http://review.couchbase.org/13592
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>

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