DEV: clean up docker detection

previously we would output stuff to console if docker.io was missing

launcher

@@ -81,7 +81,7 @@ config_file=containers/"$config".yml
 cidbootstrap=cids/"$config"_bootstrap.cid
 local_discourse=local_discourse
 image=discourse/base:2.0.20190217
-docker_path=`which docker.io || which docker`
+docker_path=`which docker.io 2> /dev/null || which docker`
 git_path=`which git`
 
 if [ "${SUPERVISED}" = "true" ]; then