Spawn a code-server instance for each test suite

This uses the current dev build by default but can be overidden with
CODE_SERVER_TEST_ENTRY (for example to test a release or some other
version).

Each instance has a separate state directory. This should make
parallelization work.

This also means you are no longer required to specify the password and
address yourself (or the extension directory once we add a test
extension). `yarn test:e2e` should just work as-is.

Lastly, it means the tests are no longer subject to yarn watch randomly
restarting.

test/utils/helpers.ts

@@ -25,7 +25,7 @@ export function createLoggerMock() {
  */
 export async function clean(testName: string): Promise<void> {
   const dir = path.join(os.tmpdir(), `code-server/tests/${testName}`)
-  await fs.rm(dir, { recursive: true })
+  await fs.rmdir(dir, { recursive: true })
 }
 
 /**