Several pyagl radio tests fail when using RTL-SDR

Several of the pyagl radio binding tests fail when using a USB RTL-SDR adapter as the radio hardware.  We somehow missed this during pyagl testing, likely because the tests pass if radio playback has been started beforehand or the test suite is run multiple times.  The root cause is due to my implementation of lazy start up of the helper application when playback is started.  That works fine in the usecase implemented with the radio application, but fails against more general use of the binding API as the tests do.