The virDomainGetMetadata function was designed to support also retrieval
of app specific metadata from the <metadata> element. This functionality
was never implemented originally.
The source code base needs to be adapted as well. Some files
include virutil.h just for the string related functions (here,
the include is substituted to match the new file), some include
virutil.h without any need (here, the include is removed), and
some require both.
