FAB-15046 Fix flaky Raft UT
FAB-15046 Fix flaky Raft UT

This makes mock Configurator in Raft UT more realistic by simulating
bi-directional link: messages can still pass through in one direction
if the link is only closed on one end.

This is particular helpful if leader reconfigures communication too
fast after committing a Raft config change to remove node. Leader should
still be able to send Step Msg to removed follower, so that follower
knows its own eviction and halts.

Change-Id: Id808737cc82a77cee93f726c5399af0aca5a7a06
Signed-off-by: Jay Guo <91d7eeb83d08be0dc56ea674009c4b53383e15b3@gmail.com>

hyperledger/fabric,muralisrini/fabric,binhn/fabric,muralisrini/fabric,manish-sethi/fabric-sidedb,stemlending/fabric,manish-sethi/fabric-sidedb,hyperledger/fabric,manish-sethi/fabric,stemlending/fabric,jimthematrix/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,binhn/fabric,manish-sethi/fabric,jimthematrix/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,stemlending/fabric,stemlending/fabric,binhn/fabric,muralisrini/fabric