MB-11686: disk I/O priority stat for bucket details
MB-11686: disk I/O priority stat for bucket details

Change-Id: I46a3f6c22f273d2c898c3a01eefc1fe4c3f85b56
Reviewed-on: http://review.couchbase.org/39532
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

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