With the (upcoming) introduction of the usb device node acl helper, which
uses policykit, spice_usbredir_channel_connect() may take a long time as
it will be waiting for the helper, which will be waiting for policykit which
may be interacting with the user. So spice_usbredir_channel_connect() will
need to become async, and since spice_usb_device_manager_connect_device
calls spice_usbredir_channel_connect it thus also needs to become async.
Note that this patch only changes spice_usb_device_manager_connect_device's
API to use the standard GIO async API, it is not actually async after this
patch since spice_usbredir_channel_connect is not yet async.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
