imgconverter: use core3 API in get_from_vm()

imgconverter/qubesimgconverter/__init__.py

@@ -172,9 +172,8 @@ get_from_stream(), get_from_vm(), get_xdg_icon_from_vm(), get_through_dvm()'''
     def get_from_vm(cls, vm, src, **kwargs):
         'Get image from VM by QUBESRPC (qubes.GetImageRGBA).'
 
-        p = vm.run('QUBESRPC qubes.GetImageRGBA dom0', passio_popen=True,
-                   gui=False)
-        p.stdin.write('{0}\n'.format(src))
+        p = vm.run_service('qubes.GetImageRGBA')
+        p.stdin.write('{0}\n'.format(src).encode())
         p.stdin.close()
 
         try: