conf: Fix even implicit labels

https://bugzilla.redhat.com/show_bug.cgi?id=1027096#c8

There are two ways in which security model can make it way into
<seclabel/>. One is as the @model attribute, the second one is
via security_driver knob in qemu.conf. Then, while parsing
<seclabel/> several checks and fix ups of old, stale combinations
are performed. However, iff @model is specified. They are not
done in the latter case. So it's still possible to feed libvirt
with senseless combinations (if qemu.conf is adjusted correctly).

One example of a seclabel that needs some adjustment (in case
security_driver=none in qemu.conf) is:

    <seclabel type='dynamic' relabel='yes'/>

The fixup code is copied from virSecurityLabelDefParseXML
(covering the former case) into virSecurityLabelDefsParseXML
(which handles the latter case).
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/conf/domain_conf.c

@@ -4974,6 +4974,13 @@ virSecurityLabelDefsParseXML(virDomainDefPtr def,
                       host->secModels[0].model);
             if (VIR_STRDUP(def->seclabels[0]->model, host->secModels[0].model) < 0)
                 goto error;
+
+            if (STREQ(def->seclabels[0]->model, "none") &&
+                flags & VIR_DOMAIN_XML_INACTIVE) {
+                /* Fix older configurations */
+                def->seclabels[0]->type = VIR_DOMAIN_SECLABEL_NONE;
+                def->seclabels[0]->relabel = false;
+            }
         } else {
             virReportError(VIR_ERR_XML_ERROR, "%s",
                            _("missing security model in domain seclabel"));