Do not update kubernetes endpoints when endpoint address count is less than or equal to master count.

checkEndpointSubsetFormat ensures that,
1. the current master's IP is in the list of addresses
2. the number of IPs in the list exactly matches the master count

This is problematic while masters are in the process of starting
because it causes frequent updates to the kubernetes endpoints until
all masters have started and added themselves to the list.

checkEndpointSubsetFormat should report success if the current
master's IP is found and the count of addresses is less than or equal
to the expected count.

pkg/master/controller_test.go

@@ -160,6 +160,54 @@ func TestReconcileEndpoints(t *testing.T) {
 				}},
 			},
 		},
+		{
+			testName:          "existing endpoints satisfy and endpoint addresses length less than master count",
+			serviceName:       "foo",
+			ip:                "4.3.2.2",
+			endpointPorts:     []api.EndpointPort{{Name: "foo", Port: 8080, Protocol: "TCP"}},
+			additionalMasters: 3,
+			endpoints: &api.EndpointsList{
+				Items: []api.Endpoints{{
+					ObjectMeta: om("foo"),
+					Subsets: []api.EndpointSubset{{
+						Addresses: []api.EndpointAddress{
+							{IP: "4.3.2.1"},
+							{IP: "4.3.2.2"},
+						},
+						Ports: []api.EndpointPort{{Name: "foo", Port: 8080, Protocol: "TCP"}},
+					}},
+				}},
+			},
+			expectUpdate: nil,
+		},
+		{
+			testName:          "existing endpoints current IP missing and address length less than master count",
+			serviceName:       "foo",
+			ip:                "4.3.2.2",
+			endpointPorts:     []api.EndpointPort{{Name: "foo", Port: 8080, Protocol: "TCP"}},
+			additionalMasters: 3,
+			endpoints: &api.EndpointsList{
+				Items: []api.Endpoints{{
+					ObjectMeta: om("foo"),
+					Subsets: []api.EndpointSubset{{
+						Addresses: []api.EndpointAddress{
+							{IP: "4.3.2.1"},
+						},
+						Ports: []api.EndpointPort{{Name: "foo", Port: 8080, Protocol: "TCP"}},
+					}},
+				}},
+			},
+			expectUpdate: &api.Endpoints{
+				ObjectMeta: om("foo"),
+				Subsets: []api.EndpointSubset{{
+					Addresses: []api.EndpointAddress{
+						{IP: "4.3.2.1"},
+						{IP: "4.3.2.2"},
+					},
+					Ports: []api.EndpointPort{{Name: "foo", Port: 8080, Protocol: "TCP"}},
+				}},
+			},
+		},
 		{
 			testName:      "existing endpoints wrong name",
 			serviceName:   "foo",