Refactor: Use cookie.sendResponse in hello_packet_executor
Refactor: Use cookie.sendResponse in hello_packet_executor

sendResponse tries to insert the packet into the already
existing write buffer and only reallocate if needed,
whereas the old method would _always_ allocate a new
send buffer.

Change-Id: I87c8134a4a8db725d9c49cf0176d6db72ee5fad9
Reviewed-on: http://review.couchbase.org/85734
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Daniel Owen <b3fc0e1a51f252986e60be7da121b74d3ac6845f@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine