Let the libvirt_open method take an optional URI parameter.
Let the libvirt_open method take an optional URI parameter.

Signed-off-by: Chris Lalancette <60b62644009db6b194cc0445b64e9b27bb26433a@redhat.com>

libvirt/ruby-libvirt,libvirt/ruby-libvirt,libvirt/ruby-libvirt