Add unit tests for delete_with_meta
Add unit tests for delete_with_meta

The following cases are covered:
1. delete_with_meta for a deleted item using an incorrect cas. Should
   fail.
2. delete_with_meta for a deleted item using the correct cas. Should
   pass.
3. delete_with_meta for a non existing item using an incorrect cas.
   Should fail.
4. delete_with_meta for a non existing item using the correct cas.
   Should pass.

Note: delete_wit_meta for an existing item was already part of the
      unit tests.

Change-Id: I2913c556ec828a95b83c0410fd1888599ea67a04
Reviewed-on: http://review.couchbase.org/15290
Tested-by: Srinivas Vadlamani <4036f57732a648e71da3ac2c829c8239a16a4c5d@couchbase.com>
Reviewed-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>
Tested-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>

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