Fix issues with mozrunner when multiple devices/emulators are on system.
- Resolve inconsistent states between device_serial argument and
DEVICE_SERIAL environment variable.
- Ignore detached or unauthorized devices when deciding which to use or
determining if selection is ambiguous.
- Fail verify_android_device if device selection is ambiguous.
Differential Revision: https://phabricator.services.mozilla.com/D239849