MB-11107: Give upr flow control stats more descriptive names
MB-11107: Give upr flow control stats more descriptive names

When debugging a flow control issue I often found myself confused
as to what some of the stats really meant. Changing the names to
be more descriptive helped me to more quickly debug issues.

Change-Id: I079b79bb6c92d7ec7b5c61c3a3aa5ad888b6d979
Reviewed-on: http://review.couchbase.org/37624
Reviewed-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>
Tested-by: Michael Wiederhold <a17fed27eaa842282862ff7c1b9c8395a26ac320@couchbase.com>

daverigby/ep-engine,sriganes/ep-engine,couchbase/ep-engine,jimwwalker/ep-engine,couchbase/ep-engine,daverigby/ep-engine,teligent-ru/ep-engine,daverigby/kv_engine,hisundar/ep-engine,daverigby/kv_engine,sriganes/ep-engine,teligent-ru/ep-engine,daverigby/ep-engine,owendCB/ep-engine,daverigby/kv_engine,daverigby/ep-engine,daverigby/kv_engine,membase/ep-engine,jimwwalker/ep-engine,membase/ep-engine,teligent-ru/ep-engine,couchbase/ep-engine,sriganes/ep-engine,membase/ep-engine,hisundar/ep-engine,owendCB/ep-engine,hisundar/ep-engine,membase/ep-engine,teligent-ru/ep-engine,jimwwalker/ep-engine,couchbase/ep-engine,sriganes/ep-engine,hisundar/ep-engine,owendCB/ep-engine,jimwwalker/ep-engine,owendCB/ep-engine