domain_conf: Introduce VIR_DOMAIN_DEF_PARSE_SKIP_POST_PARSE
    
    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: Michal Privoznik <mprivozn@redhat.com>