Merge "Add README for test using two emulators."

* Under android root, `source build/envsetup.sh`

* 'lunch gcar_emu_x86_64-userdebug'

* `lunch gcar_emu_x86_64-userdebug`

* `m -j`

* Run the emulator:

* Run the emulator, the '-read-only' flag is required to run multiple instances:

  `aae emulator run`

  `aae emulator run -read-only`

* The android lunch target: gcar_emu_x86_64-userdebug and

  cf_x86_64_auto-userdebug already contains the default remote access HAL. For

* Now you can issue `ctrl c` on the first adb shell to stop the test wakeup

  client.

## How to build and test the test wakeup client using two gcar emulators.

In this test case, we are going to use two gcar emulators, one as the

Application Processor, one as the TCU.

* Change the IP address to allow IP communication between different emulator

  instances. For detail about why we change it this way, see [interconnecting

  emulator instance](https://developer.android.com/studio/run/emulator-networking#connecting).

  Change 'DGRPC_SERVICE_ADDRESS' in `test_grpc_server/Android.bp` to

  `10.0.2.15:50051`.

  Change `DGRPC_SERVICE_ADDRESS` in 'hal/defaut/Android.bp' to

  `10.0.2.2:50051`.

* Under android root: `source build/envsetup.sh`

* `lunch gcar_emu_x86_64-userdebug`

*  `m -j`

* Start one gcar emulator as TCU

  `aae emulator run -read-only`

* Start a new shell session. Connect to the emulator's console,

  see [Start and stop a console session](https://developer.android.com/studio/run/emulator-console#console-session)

  for detail.

  `telnet localhost 5554`

* `auth auth_token` where auth_token must match the contents of the

  `.emulator_console_auth_token` file.

* `redir add tcp:50051:50051`

* Exit the telnet session

 Make the target device writable:

  `adb root`

  `adb remount`

  `adb reboot`

  `adb root`

  `adb remount`

* `make -j TestWakeupClientServer`

* `cd out/target/product/emulator_car64_x86_64/`

* `adb push vendor/bin/TestWakeupClientServer /vendor/bin`

* `adb shell`

* `su`

* `/vendor/bin/TestWakeupClientServer`

* Start a new shell, start another gcar emulator as the Application Processor:

  `aae emulator run -read-only`

* Connect to adb shell for the application processor:

  `adb -s emulator-5556 shell`

  `su`

* Follow the test instructions for one gcar emulator using the 'dumpsys'

  commands.