stbt-control-relay: Add --timeout argument
stbt-control-relay: Add --timeout argument

Exits (with successful status) if no commands are received within that
time. We have seen libcec get into a funny state with the Amazon Fire TV
Stick if it's idle for a long time. This is intended to be used in
combination with systemd socket-activation and Restart=on-failure.

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