kvm: Switch default and kvm-cluster to json-in-xml

default and kvm-cluster software types are now json-in-xml, so they accept
and return json-in-xml.

Update tests to show that xml and json-in-xml serialization works.

Note: There was invective to publish with pure XML serialisation, but it is
wrong idea because:

 1) serialisation in the software.cfg.json is provided for both ways
 2) requesting instances with given serialisation by profiles expect same
    serialisation

Request resilient instances with serialised, as they reply with json-in-xml.