Use 'DcpConsumer' ptr in consumer 'Processor' than the base class ptr
Use 'DcpConsumer' ptr in consumer 'Processor' than the base class ptr

DCPConsumer creates a 'Processor' task which is used exclusively
only by it. The object however has a RCPtr to the base class
'ConnHandler' and the 'Processor' object dynamically casts the
'ConnHandler' ptr to 'DCPConsumer' ptr.

This commit uses the 'DCPConsumer' RCPtr to avoid unnecessary
dynamic casts.

Change-Id: Ic58d46d391baf2d477338f445dc4ed6c5c490ae6
Reviewed-on: http://review.couchbase.org/85213
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

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