Commit e6e4ff4c

 fixed Issue 649 by switching the
separator for usb_devices from comma to space. That solved the problem with
the command line, but RAPI was able to work with commas too, so, for backwards
compatibility we need to keep supporting that as well.

Also, in order to avoid changing the format of the config file, the default
internal representation is brought back to being comma-based, and it is changed
at the interface level (CLI or RAPI) before being passed on.

Signed-off-by: Michele Tartara <mtartara@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>