Implemented the ability to allocate SpiceUsbDevice instances

by passing an open file descriptor in order to support the modern
Android USB device permissioning scheme.

During the process, a handle obtained by a call to
libusb_wrap_sys_device() is stored in the SpiceUsbDevice instance.

A call to libusb_open() is skipped if there is already a handle
present in the SpiceUsbDevice instance.

Finally, on Android, the option LIBUSB_OPTION_NO_DEVICE_DISCOVERY
must be set prior to the call to libusb_init() as per libusb
documentation.
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