Implement Device Timeout

[JakeWharton]

Have a per-device timer of an arbitrary value (say, 5m) which gets reset on every ddmlib callback (e.g., test started, test run started, test failed, etc.) that will interrupt execution if a timeout occurs.

[JakeWharton]

This can only reliably be done with process killing where the main process monitors events via IPC from all the per-device processes.