[FAB-12709] Enable CheckQuorum

When CheckQuorum is enabled, leader steps down if it cannot reach
the quorum of network, so that clients have a chance to disconnect
and try other nodes.

Change-Id: I901c0e3009f9d354a2b504fe16174432345055b3
Signed-off-by: Jay Guo <guojiannan1101@gmail.com>

orderer/consensus/etcdraft/chain.go

@@ -201,6 +201,7 @@ func NewChain(
 		// PreVote prevents reconnected node from disturbing network.
 		// See etcd/raft doc for more details.
 		PreVote:                   true,
+		CheckQuorum:               true,
 		DisableProposalForwarding: true, // This prevents blocks from being accidentally proposed by followers
 	}
 

orderer/consensus/etcdraft/chain_test.go

@@ -1891,6 +1891,28 @@ var _ = Describe("Chain", func() {
 				})
 			})
 
+			When("leader is disconnected", func() {
+				It("proactively steps down to follower", func() {
+					network.disconnect(1)
+
+					By("Ticking leader until it steps down")
+					Eventually(func() <-chan raft.SoftState {
+						c1.clock.Increment(interval)
+						return c1.observe
+					}, LongEventualTimeout).Should(Receive(Equal(raft.SoftState{Lead: 0, RaftState: raft.StateFollower})))
+
+					By("Ensuring it does not accept message due to the cluster being leaderless")
+					err := c1.Order(env, 0)
+					Expect(err).To(MatchError("no Raft leader"))
+
+					network.elect(2)
+					network.join(1, true)
+
+					err = c1.Order(env, 0)
+					Expect(err).NotTo(HaveOccurred())
+				})
+			})
+
 			When("follower is disconnected", func() {
 				It("should return error when receiving an env", func() {
 					network.disconnect(2)