This change set adds cluster communication metrics:

	EgressQueueSize          metrics.Gauge
	EgressWorkerCount        metrics.Gauge
	IngressStreamsCount      metrics.Gauge
	EgressStreamsCount       metrics.Gauge
	EgressTLSConnectionCount metrics.Gauge
	MessageSendTime          metrics.Histogram
	MessagesDroppedCount     metrics.Counter

And adds corresponding unit tests for them.

Change-Id: I769d83b0721cc8dbf35b07b51b1d024539064009
Signed-off-by: yacovm <yacovm@il.ibm.com>
(cherry picked from commit 37fc516d6465be36c4e3daabd612155b9c2c18d3)