qemu-iotests: skip test 005 for vpc format images

The vpc format doesn't support large enough image size for this test.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/005

@@ -43,10 +43,13 @@ trap "_cleanup; exit \$status" 0 1 2 3 15
 . ./common.rc
 . ./common.filter
 
-# vpc is limited to 127GB, so we can't test it here
 _supported_fmt generic
 _supported_os Linux
 
+# vpc is limited to 127GB, so we can't test it here
+if [ "$IMGFMT" = "vpc" ]; then
+    _notrun "image format $IMGFMT does not support large image sizes"
+fi
 
 echo
 echo "creating large image"