qemublocktest: XMLjsonXML: Test formatting/parsing of modern JSON
qemublocktest: XMLjsonXML: Test formatting/parsing of modern JSON

The test was invoking the JSON formatter with the 'legacy' flag thus
formatting bunch of obsolete JSON blockdev definitions. We also should
test the modern ones. Add a boolean and re-run all the tests in both
cases.

Additionally for any modern invocation we should also validate that the
output conforms to the QAPI schema.

Signed-off-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

crobinso/libvirt,jardasgit/libvirt,jfehlig/libvirt,nertpinx/libvirt,jfehlig/libvirt,libvirt/libvirt,jardasgit/libvirt,jfehlig/libvirt,crobinso/libvirt,fabianfreyer/libvirt,zippy2/libvirt,jardasgit/libvirt,zippy2/libvirt,fabianfreyer/libvirt,zippy2/libvirt,crobinso/libvirt,jardasgit/libvirt,nertpinx/libvirt,nertpinx/libvirt,libvirt/libvirt,crobinso/libvirt,zippy2/libvirt,jardasgit/libvirt,olafhering/libvirt,libvirt/libvirt,libvirt/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,olafhering/libvirt,olafhering/libvirt,fabianfreyer/libvirt,olafhering/libvirt,nertpinx/libvirt