test(@angular-devkit/build-angular): add karma@5.2 E2E test

This test ensures that karma 5.2.x will continue to function in addition to the new 6.x default.

tests/legacy-cli/e2e/tests/test/test-karma-5.ts

@@ -0,0 +1,11 @@
+import { ng } from '../../utils/process';
+import { installPackage } from '../../utils/packages';
+
+/**
+ * Ensure karma 5.2 continues to function
+ */
+export default async function () {
+  await installPackage('karma@5.2');
+
+  await ng('test', '--watch=false');
+}