[leader_activities] Pass the activity token to add_activity.
[leader_activities] Pass the activity token to add_activity.

Again, to reduce number of arguments passed around.

Change-Id: Ifeabd88597d0ce1072b858ba7405ae216aecc0b3
Reviewed-on: http://review.couchbase.org/89578
Reviewed-by: Poonam Dhavale <6855f09986fe28ed7e8cdd9d60db878d898703d5@couchbase.com>
Tested-by: Aliaksey Artamonau <ce14b1c16e0fd654f926118eb8addbec5aff4ffa@couchbase.com>

membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server