add external resource group support for azure disk

fix naming issue

fix comments

pkg/cloudprovider/providers/azure/azure_test.go

@@ -2699,3 +2699,39 @@ func TestCanCombineSharedAndPrivateRulesInSameGroup(t *testing.T) {
 // func TestIfServiceIsEditedFromSharedRuleToOwnRuleThenItIsRemovedFromSharedRuleAndOwnRuleIsCreated(t *testing.T) {
 // 	t.Error()
 // }
+
+func TestGetResourceGroupFromDiskURI(t *testing.T) {
+	tests := []struct {
+		diskURL        string
+		expectedResult string
+		expectError    bool
+	}{
+		{
+			diskURL:        "/subscriptions/4be8920b-2978-43d7-axyz-04d8549c1d05/resourceGroups/azure-k8s1102/providers/Microsoft.Compute/disks/andy-mghyb1102-dynamic-pvc-f7f014c9-49f4-11e8-ab5c-000d3af7b38e",
+			expectedResult: "azure-k8s1102",
+			expectError:    false,
+		},
+		{
+			diskURL:        "/4be8920b-2978-43d7-axyz-04d8549c1d05/resourceGroups/azure-k8s1102/providers/Microsoft.Compute/disks/andy-mghyb1102-dynamic-pvc-f7f014c9-49f4-11e8-ab5c-000d3af7b38e",
+			expectedResult: "",
+			expectError:    true,
+		},
+		{
+			diskURL:        "",
+			expectedResult: "",
+			expectError:    true,
+		},
+	}
+
+	for _, test := range tests {
+		result, err := getResourceGroupFromDiskURI(test.diskURL)
+		assert.Equal(t, result, test.expectedResult, "Expect result not equal with getResourceGroupFromDiskURI(%s) return: %q, expected: %q",
+			test.diskURL, result, test.expectedResult)
+
+		if test.expectError {
+			assert.NotNil(t, err, "Expect error during getResourceGroupFromDiskURI(%s)", test.diskURL)
+		} else {
+			assert.Nil(t, err, "Expect error is nil during getResourceGroupFromDiskURI(%s)", test.diskURL)
+		}
+	}
+}