Fix XmlStreamUtils writing attributes.

The prefix for attributes was no set.
This would result in an exception when no prefix was available by default.

Using RandomPrefix now.

Change-Id: I6110293b262a77f987534fe98abf51755a066be0
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>
Merge "Fix XmlStreamUtils writing attributes."