qemu: fix cannot set graphic passwd via qemuDomainSaveImageDefineXML

https://bugzilla.redhat.com/show_bug.cgi?id=1183890

When we try to update a xml to a image file, we will clear the
graphics passwd settings, because we do not pass VIR_DOMAIN_XML_SECURE
to qemuDomainDefCopy, qemuDomainDefFormatBuf won't format the passwd.

Add VIR_DOMAIN_XML_SECURE flag when we call qemuDomainDefCopy
in qemuDomainSaveImageUpdateDef.
Signed-off-by: NLuyao Huang <lhuang@redhat.com>

src/qemu/qemu_driver.c

@@ -5623,7 +5623,8 @@ qemuDomainSaveImageUpdateDef(virQEMUDriverPtr driver,
 
     if (!(newdef_migr = qemuDomainDefCopy(driver,
                                           newdef,
-                                          VIR_DOMAIN_XML_MIGRATABLE)))
+                                          VIR_DOMAIN_XML_MIGRATABLE |
+                                          VIR_DOMAIN_XML_SECURE)))
         goto cleanup;
 
     if (!virDomainDefCheckABIStability(def, newdef_migr)) {