MB-21190: update log message for set max_cas
MB-21190: update log message for set max_cas

There's a future desire to print vbucket's as "vb:"

Change-Id: I5ac58daa01a1dd2ed5a631558bf735c9a81ed821
Reviewed-on: http://review.couchbase.org/68994
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

membase/ep-engine,membase/ep-engine,membase/ep-engine,couchbase/ep-engine,daverigby/kv_engine,membase/ep-engine,daverigby/ep-engine,daverigby/ep-engine,couchbase/ep-engine,couchbase/ep-engine,couchbase/ep-engine,daverigby/ep-engine,daverigby/ep-engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine