AccessoryConnectionBootstrap: close everything in disconnect()

Fixes a problem after physical disconnect: IOIOImpl.disconnected()
detects a physical disconnect and tells the IOIOConnection about it by
calling disconnect().  AccessoryConnectionBootstrap's implementation
of it however only adjusts its internal state without closing the
connection, leaving a disconnected file descriptor which will be
reused for the next connect attempt.  In the end, we get ENODEV
repeatedly because the IOIO device is long gone.

By forwarding Connection.disconnect() to
AccessoryConnectionBootstrap.close(), AccessoryConnectionBootstrap's
state is adjusted as well, and a new device is opened next time.