debugutils: fix enum/flag properties printing for elements
debugutils: fix enum/flag properties printing for elements

We want to use the flag/enum nicks here, not only because they
are shorter but also because in case of element-specific enums
and flags we abuse the enum/flag name field for the description,
and we don't want that printed in the dot file.

https://bugzilla.gnome.org/show_bug.cgi?id=763814

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