This also lets us remove the call to dfu_device_wait_for_replug() which was
causing a deadlock due to unsafe main context usage. Splitting the code allows
us to use the device list to watch for replug, without adding even more Jabra-
specific plugin code to the DFU plugin.
Looking at this with a 40,000ft view, the Jabra runtime really doesn't have
much in common with DFU and the reason it was originally all lumped together
was that the daemon couldn't "change" plugins between detach and update.
It's unfortunate that we have to include a sleep() in the DFU code after the
DFU probe, but this is specified by Jabra themselves. Attempting to open the
device without waiting reboots the hub back into runtime firmware mode, so we
can't even retry the failing setup action.
