Camera1 CTS: Check for external cameras

- Make sure at least one camera is listed by the camera service when the
  android.hardware.camera.external feature is defined.
- Make sure all listed cameras can be opened (and are therefore plugged in)
  when the android.hardware.camera.external feature is defined.

Change-Id: Id43bc3c008cc533d890f5f5a8c2f09af8f4be5a7
2 files changed