use test callback from test form save hooks

Enter key and other form submits are handled generically from the built-in
save hooks on the form controller. This adds implementations for those hooks
on the plugin test forms to make sure the expected handlers are always called.

awx/ui/client/features/credentials/external-test-modal.component.js

@@ -5,6 +5,10 @@ function ExternalTestModalController (strings) {
 
     vm.strings = strings;
     vm.title = strings.get('externalTest.TITLE');
+
+    vm.$onInit = () => {
+        vm.form.save = () => vm.onSubmit();
+    };
 }
 
 ExternalTestModalController.$inject = [

awx/ui/client/features/credentials/input-source-lookup.component.js

@@ -6,7 +6,10 @@ function InputSourceLookupController (strings, wait) {
     vm.strings = strings;
     vm.title = strings.get('inputSources.TITLE');
 
-    vm.$onInit = () => wait('start');
+    vm.$onInit = () => {
+        wait('start');
+        vm.form.save = () => vm.onTest();
+    };
 
     vm.onReady = () => {
         vm.isReady = true;