clean-docker: adjust for non-GNU

bin/clean-docker

@@ -1,6 +1,14 @@
 #!/bin/sh
+if [ "$(xargs --version | grep GNU)" != "" ] ; then
+  echo GNU xargs
+  export XARGS_ARG="--no-run-if-empty"
+else
+  echo Not GNU xargs
+  export XARGS_ARG=""
+fi
+
 echo "Removing exited containers."
-docker ps -a | grep Exited | awk '{print $NF}' | xargs --no-run-if-empty docker rm
+docker ps -a | grep Exited | awk '{print $NF}' | xargs $XARGS_ARG docker rm
 
 echo "Removing unused images."
-docker images -q --filter "dangling=true" | xargs --no-run-if-empty docker rmi
+docker images -q --filter "dangling=true" | xargs $XARGS_ARG docker rmi