AdbDevice.devices: Don't need to catch CalledProcessError
AdbDevice.devices: Don't need to catch CalledProcessError

...because we don't specify `check=True`.

Also use subprocess's `encoding` parameter.

stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester