object: Add _set_name() test on parented object
object: Add _set_name() test on parented object

This is not allowed, and set_name() should fail.

https://bugzilla.gnome.org/show_bug.cgi?id=766923

StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer