security: don't fail if built without attr support

If built without attr support removing any image will trigger
 qemuBlockRemoveImageMetadata (the one that emits the warning)
   -> qemuSecurityMoveImageMetadata
     -> virSecurityManagerMoveImageMetadata
       -> virSecurityDACMoveImageMetadata
         -> virSecurityDACMoveImageMetadataHelper
           -> virProcessRunInFork (spawns subprocess)
             -> virSecurityMoveRememberedLabel

In there due to !HAVE_LIBATTR virFileGetXAttrQuiet will return
ENOSYS and from there the chain will error out.

That is wrong and looks like:
  libvirtd[6320]: internal error: child reported (status=125):
  libvirtd[6320]: Unable to remove disk metadata on vm testguest from
  /var/lib/uvtool/libvirt/images/testguest.qcow (disk target vda)

This change makes virSecurityDACMoveImageMetadataHelper and
virSecuritySELinuxMoveImageMetadataHelper accept that
error code gracefully and in that sense it is an extension of:
5214b2f1a3 "security: Don't skip label restore on file systems lacking XATTRs"
which does the same for other call chains into the virFile*XAttr functions.

Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

src/security/security_dac.c

@@ -1117,6 +1117,12 @@ virSecurityDACMoveImageMetadataHelper(pid_t pid G_GNUC_UNUSED,
 
     ret = virSecurityMoveRememberedLabel(SECURITY_DAC_NAME, data->src, data->dst);
     virSecurityManagerMetadataUnlock(data->mgr, &state);
+
+    if (ret == -2) {
+        /* Libvirt built without XATTRS */
+        ret = 0;
+    }
+
     return ret;
 }
 

src/security/security_selinux.c

@@ -1975,6 +1975,12 @@ virSecuritySELinuxMoveImageMetadataHelper(pid_t pid G_GNUC_UNUSED,
 
     ret = virSecurityMoveRememberedLabel(SECURITY_SELINUX_NAME, data->src, data->dst);
     virSecurityManagerMetadataUnlock(data->mgr, &state);
+
+    if (ret == -2) {
+        /* Libvirt built without XATTRS */
+        ret = 0;
+    }
+
     return ret;
 }