use proc_lib to spawn slow_updater of ns_heart
use proc_lib to spawn slow_updater of ns_heart

I.e. so that if it dies we have some diagnostics

Change-Id: I73b721a2e1a561a4ee1e49a663540414a8cf5ac4
Reviewed-on: http://review.couchbase.org/30349
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>

ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,mschoch/ns_server,mschoch/ns_server,daverigby/ns_server,daverigby/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,daverigby/ns_server,ceejatec/ns_server,nimishzynga/ns_server,membase/ns_server,mschoch/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,daverigby/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,membase/ns_server,daverigby/ns_server,membase/ns_server,membase/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server