ooiion-1361 Platform Agent should transition child devices into autosample mode

... when it receives the start_autosample command. Add ops in PlatformAgent consistent with pattern to allow start_autosample/stop_autosample to be recursive in the same way that other commands are propogated to child devices. Add test to verify that the child devices enter streaming mode then exit as expected.


@edwardhunter  please review