More robust check to see if ADB is running

Faster, more robust check to see if ADB is running on bootup. Opens a socket for port 5037 and asks for "host:version" (which is exactly what the ADB commandline client does). If only I knew about this earlier, I wouldn't have wasted a bunch of time getting that `ps` solution working.

@ochameau This is better than using `ps` or `taskList.exe` right?