tests: introduce create_client()

Introduce a new helper create_client(), which creates and initializes
the client struct, but does not create a wl_surface.

This will be useful for ivi-shell tests.

v2: Rebased, and restored the dependency to weston-test.so, since seat
handling requires it.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Marek Chalupa <mchqwerty@gmail.com>
diff --git a/tests/weston-test-client-helper.h b/tests/weston-test-client-helper.h
index 63883fe..61c0b45 100644
--- a/tests/weston-test-client-helper.h
+++ b/tests/weston-test-client-helper.h
@@ -144,6 +144,9 @@
 }
 
 struct client *
+create_client(void);
+
+struct client *
 client_create(int x, int y, int width, int height);
 
 struct wl_buffer *