Fix OSC_DEVNO. It was set initially in the inferior environment variable

Fix OSC_DEVNO.  It was set initially in the inferior environment variable
config method, but we can name devices now.  It is still convenient to
save this value to avoid having to get it for each test.  Maybe the
--thread and --device code can be changed to support device names directly
(if they don't already by virtue of using the same device setup code).