Fix a bug in dsync initialization and communication (#5428)

In current implementation we used as many dsync clients
as per number of endpoints(along with path) which is not
the expected implementation. The implementation of Dsync
was expected to be just for the endpoint Host alone such
that if you have 4 servers and each with 4 disks we need
to only have 4 dsync clients and 4 dsync servers. But
we currently had 8 clients, servers which in-fact is
unexpected and should be avoided.

This PR brings the implementation back to its original
intention. This issue was found #5160

cmd/lock-rpc-server_test.go

@@ -425,8 +425,8 @@ func TestLockRpcServerExpired(t *testing.T) {
 	}
 }
 
-// Test initialization of lock servers.
-func TestLockServers(t *testing.T) {
+// Test initialization of lock server.
+func TestLockServerInit(t *testing.T) {
 	if runtime.GOOS == globalWindowsOSName {
 		return
 	}
@@ -438,8 +438,10 @@ func TestLockServers(t *testing.T) {
 	defer os.RemoveAll(rootPath)
 
 	currentIsDistXL := globalIsDistXL
+	currentLockServer := globalLockServer
 	defer func() {
 		globalIsDistXL = currentIsDistXL
+		globalLockServer = currentLockServer
 	}()
 
 	case1Endpoints := mustGetNewEndpointList(
@@ -468,26 +470,27 @@ func TestLockServers(t *testing.T) {
 
 	globalMinioHost = ""
 	testCases := []struct {
-		isDistXL         bool
-		endpoints        EndpointList
-		totalLockServers int
+		isDistXL  bool
+		endpoints EndpointList
 	}{
 		// Test - 1 one lock server initialized.
-		{true, case1Endpoints, 1},
-		// Test - 2 two servers possible.
-		{true, case2Endpoints, 2},
+		{true, case1Endpoints},
+		// Test - similar endpoint hosts should
+		// converge to single lock server
+		// initialized.
+		{true, case2Endpoints},
 	}
 
 	// Validates lock server initialization.
 	for i, testCase := range testCases {
 		globalIsDistXL = testCase.isDistXL
-		globalLockServers = nil
+		globalLockServer = nil
 		_, _ = newDsyncNodes(testCase.endpoints)
 		if err != nil {
 			t.Fatalf("Got unexpected error initializing lock servers: %v", err)
 		}
-		if len(globalLockServers) != testCase.totalLockServers {
-			t.Fatalf("Test %d: Expected total %d, got %d", i+1, testCase.totalLockServers, len(globalLockServers))
+		if globalLockServer == nil && testCase.isDistXL {
+			t.Errorf("Test %d: Expected initialized lockServer, but got uninitialized", i+1)
 		}
 	}
 }