[USB] usbtest, add more tests; minor fixes

More tests for host and gadget controller drivers:

    - test 13, bulk endpoint halts
    - test 14, control OUT transfers
    - test 15, iso OUT testing
    - test 16, iso IN testing

Other improvements:
    - Many tests now support data pattern testing submodes.
    - Use the standard usb_set_interface() call, not its own
      version ... one more API call covered!
    - Converted to use driver model style diagnostics.

And minor fixes.