Add waylandsink fullscreen support

With /etc/xdg/weston/weston.ini set the display mode to 720p, we need to
enable the fullscreen support so the display will not get cut off

Tested: edgetpu_{detect, classify, demo}
Change-Id: I06e434369ce9076902e71c009a25484d0532e333
diff --git a/edgetpuvision/gstreamer.py b/edgetpuvision/gstreamer.py
index 7d0d4ee..58e6ae4 100644
--- a/edgetpuvision/gstreamer.py
+++ b/edgetpuvision/gstreamer.py
@@ -340,6 +340,8 @@
         # drawing_area.realize()
 
         glsink = pipeline.get_by_name('glsink')
+        if display is Display.FULLSCREEN:
+          glsink.set_property('fullscreen', True)
 
         # window.connect('delete-event', Gtk.main_quit)
         # window.show_all()