This is an internal flag that prevents our two entry points to
XML parsing (virDomainDefParse and virDomainDeviceDefParse) from
running post parse callbacks. This is expected to be used in
cases when we already have full domain/device XML and we are just
parsing it back (i.e. virDomainDefCopy or virDomainDeviceDefCopy)
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>