Commit 0696071316 moved away from QDom but
also lost the ability to fill the introspection field of the created
QDBusIntrospection::Interface instances. This commit now generate the
string again as we proceed with the QXmlStreamReader based parsing.
Task-number: QTBUG-26668
Change-Id: I8f406e1f4e9d3e667a8557db69da36cac369ba4f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>