MB-11902: Always set dtype value to zero

In 3.0 release, server won't handle dtype value other than 0. Besides,
disable hello command because it is not supported in 3.0 yet.

Change-Id: I898aa8596d6b00c25072f18e579b98a3fe877af3
Reviewed-on: http://review.couchbase.org/40388
Tested-by: Bin Cui <bin.cui@gmail.com>
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>