glupload: Only renegotiate if the caps are incompatible

There is new code that ensures that we renegotiate after an
uploader transition if the negotiated caps have changed.

The problem is that the raw uploader will not really try and
fixate the input caps, but instead of return a subset with the
only the supported target texture.

This had two effect, raw uploads was always done renegotiated
once and the raw upload unit test was now failing as it didn't
expect a renegotiation.

As it's a valid check, simply relax the gst_caps_is_equal() check
and use a gst_caps_is_subset() instead.

https://bugzilla.gnome.org/show_bug.cgi?id=783521

gst-libs/gst/gl/gstglupload.c

@@ -2015,7 +2015,7 @@ restart:
     if (last_impl != upload->priv->method_impl) {
       GstCaps *caps = gst_gl_upload_transform_caps (upload, upload->context,
           GST_PAD_SINK, upload->priv->in_caps, NULL);
-      if (!gst_caps_is_equal (upload->priv->out_caps, caps)) {
+      if (!gst_caps_is_subset (caps, upload->priv->out_caps)) {
         gst_buffer_replace (&outbuf, NULL);
         ret = GST_GL_UPLOAD_RECONFIGURE;
       }