JVMCBC-48: Populate CAS into RemoveResponse

Motivation
----------
The server returns the CAS value together with other information on a remove
response, so the actual RemoveResponse object should reflect that.

Modifications
-------------
The decoded cas value is passed into the RemoveResponse object, integration
test have been extended to verify the expected behavior.

Result
------
The CAS value is now accessible from the RemoveResponse

Change-Id: I94b5dbc3b406c02b012090b6be3ea475306ad1c0
Reviewed-on: http://review.couchbase.org/42342
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>