Fix ensureStaticIP if name for existed address was changed

It might happend when we change external IP address from ephemeral to
static and give it a custom name.
In this case GetRegionAddress with given name will return Not Found

Author: Elena Morozova

staging/src/k8s.io/legacy-cloud-providers/gce/gce_loadbalancer_external.go

@@ -1060,6 +1060,18 @@ func ensureStaticIP(s CloudAddressService, name, serviceName, region, existingIP
 		existed = true
 	}
 
+	// If address exists, get it by IP, because name might be different.
+	// This can specifically happen if the IP was changed from ephemeral to static,
+	// which results in a new name for the IP.
+	if existingIP != "" {
+		addr, err := s.GetRegionAddressByIP(region, existingIP)
+		if err != nil {
+			return "", false, fmt.Errorf("error getting static IP address: %v", err)
+		}
+		return addr.Address, existed, nil
+	}
+
+	// Otherwise, get address by name
 	addr, err := s.GetRegionAddress(name, region)
 	if err != nil {
 		return "", false, fmt.Errorf("error getting static IP address: %v", err)

staging/src/k8s.io/legacy-cloud-providers/gce/gce_loadbalancer_external_test.go

@@ -63,6 +63,13 @@ func TestEnsureStaticIP(t *testing.T) {
 	if err != nil || !existed || ip != ipPrime {
 		t.Fatalf(`ensureStaticIP(%v, %v, %v, %v, %v) = %v, %v, %v; want %v, true, nil`, gce, ipName, serviceName, gce.region, ip, ipPrime, existed, err, ip)
 	}
+
+	// Ensure call with different name
+	ipName = "another-name-for-static-ip"
+	ipPrime, existed, err = ensureStaticIP(gce, ipName, serviceName, gce.region, ip, cloud.NetworkTierDefault)
+	if err != nil || !existed || ip != ipPrime {
+		t.Fatalf(`ensureStaticIP(%v, %v, %v, %v, %v) = %v, %v, %v; want %v, true, nil`, gce, ipName, serviceName, gce.region, ip, ipPrime, existed, err, ip)
+	}
 }
 
 func TestEnsureStaticIPWithTier(t *testing.T) {