tests: Use ostree commit --consume

Just noticed this while working on something else; we should use it where
possible.

Closes: #1117
Approved by: jlebon

tests/vmcheck/overlay.sh

@@ -65,6 +65,14 @@ fi
 rm -vrf vmcheck/usr/etc/selinux/targeted/semanage.*.LOCK
 # ✀✀✀ END tmp hack
 
-ostree commit --parent=none -b vmcheck --add-metadata-string=ostree.source-title="Dev overlay on ${origin}" --add-metadata-string=rpmostree.original-origin=${origin} --link-checkout-speedup \
-  --selinux-policy=vmcheck --tree=dir=vmcheck
+consume_opt=
+if ostree commit --help | grep -q -e --consume; then
+    consume_opt=--consume
+fi
+
+ostree commit --parent=none -b vmcheck \
+       --add-metadata-string=ostree.source-title="Dev overlay on ${origin}" \
+       --add-metadata-string=rpmostree.original-origin=${origin} \
+       --link-checkout-speedup ${consume_opt} \
+       --selinux-policy=vmcheck --tree=dir=vmcheck
 ostree admin deploy vmcheck