tests: add frame callback waiting helpers

To avoid duplicating the code for setting and waiting for a frame
callback, add helpers for it.

Convert move_client() to use the new helpers.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/tests/weston-test-client-helper.h b/tests/weston-test-client-helper.h
index 27042b2..c576dcd 100644
--- a/tests/weston-test-client-helper.h
+++ b/tests/weston-test-client-helper.h
@@ -111,4 +111,10 @@
 	assert(wl_display_roundtrip((c)->wl_display) >= 0); \
 } while (0)
 
+struct wl_callback *
+frame_callback_set(struct wl_surface *surface, int *done);
+
+void
+frame_callback_wait(struct client *client, int *done);
+
 #endif