Medium: xml: Bug bnc#552713 - Treat node unames as text fields not IDs
Because it is normal for the nodes section to be empty for new clusters
there is effectively nowhere it can be used as an IDREF to provide
additional validation.
Combined with the problem of enforcing XML's rules for ID fields on our
host names (ie. can't start with an integer), we're better off making it
a regular text field.

Mercurial revision: 06061a6bb14123309ac164ea113443246ec52901