Android lint error when upgrade to Android plugin 4.x

Trying to upgrade Android plugin to 4.x as described in https://github.com/grpc/grpc-java/issues/8421#issue-973899271 with some minor workarounds, the build failed with a lint error:

```
FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':grpc-android-interop-testing:lint'.
> Lint found errors in the project; aborting build.

Fix the issues identified by lint, or add the following to your build script to proceed with errors:
...
android {
lintOptions {
abortOnError false
}
}
...
Errors found:

/Users/zdapeng/git/grpc-java/android-interop-testing/src/main/AndroidManifest.xml:23: Error: Class referenced in the manifest, io.grpc.binder.HostServices$HostService1, was not found in the project or the libraries [MissingClass]

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/zdapeng/git/grpc-java/android-interop-testing/src/main/AndroidManifest.xml:24: Error: Class referenced in the manifest, io.grpc.binder.HostServices$HostService2, was not found in the project or the libraries [MissingClass]

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

android-interop-testing/src/main/AndroidManifest.xml と HostServices$HostService1 および HostServices$HostService2 の lint 失敗から始めます。リンクされた issue で Android plugin 4.x へのアップグレードの背景を確認してから、Android lint task を実行します。manifest の参照が解決され、lint task が MissingClass エラーなしで完了すれば完了です。

索引モデルが issue の本文から書いたものです。