Add an option to share connection and channel between Samplers.

[rbnxx]

In a test case with X samplers (AMQPPublisher or AMQPConsumer) connected to the same broker, if "Share Channel" is enabled, JMeter will open only 1 connection to the broker for each user independently (instead of opening 1 connection per Sampler and per user).

Note: connection will be closed by the first Sampler cleanup code, cleanup code for other Samplers sharing the same connection won't be correctly executed.