Centralize credential handling

My thinking is that this may reduce the cognitive overhead for
developers writing new test suites.

This also allows us to perform different setup steps (like ensuring the
editor is visible when authenticated).

test/e2e/models/CodeServer.ts

@@ -250,8 +250,12 @@ export class CodeServerPage {
    *
    * It is recommended to run setup before using this model in any tests.
    */
-  async setup() {
+  async setup(authenticated: boolean) {
     await this.navigate()
-    await this.reloadUntilEditorIsReady()
+    // If we aren't authenticated we'll see a login page so we can't wait until
+    // the editor is ready.
+    if (authenticated) {
+      await this.reloadUntilEditorIsReady()
+    }
   }
 }