Return Status::UnknownCommand for commands without validator
Return Status::UnknownCommand for commands without validator

All commands currently have packet validators (and we want
to keep it that way), return "Unknown Command" for packets
received where there isn't a packet validator.

Change-Id: I3ed1accb7bb76a4bd649fa1cccff1866929f5a78
Reviewed-on: http://review.couchbase.org/102154
Well-Formed: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Paolo Cocchi <9dd88c9f3e5cbab6e19a6c020f107e0c648ac956@couchbase.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

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