Move Item member initialization to initializer list
Move Item member initialization to initializer list

More refactoring to prepare for merging consturctors, also is more
efficient as we don't default construct the std::string for key before
assigning it.

Change-Id: I3c6e45ea9f3303e5d29f7231ae282f1d59efb31c
Reviewed-on: http://review.couchbase.org/42624
Reviewed-by: Michael Wiederhold <a17fed27eaa842282862ff7c1b9c8395a26ac320@couchbase.com>
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>
Reviewed-by: abhinav dangeti <d73ef2279de6577f7bf081737ee47554bbb7dc82@couchbase.com>
Tested-by: abhinav dangeti <d73ef2279de6577f7bf081737ee47554bbb7dc82@couchbase.com>

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