Added a new configuration option `send_single_reply` which allows to
send a single AMQP reply instead of two. This will reduce amount of RPC
calls and increase transport productivity.
The new behaviour is not compatible with the old logic, so isn't
backward compatible and disabled by default.
DocImpact
A new configuration option added.
Blueprint: remove-double-reply
Change-Id: Idab118b22163e734aca010f325cddfaec26bfa0f