F #4089: Add DH distro parameter and root user (#4888)

src/datastore_mad/remotes/docker_downloader.sh

@@ -142,9 +142,11 @@ mkdir -p $dockerdir
 mkdir -p $dockerdir/mnt
 
 # Check distro
+if [ -z $distro ]; then
 distro=`docker run --rm \
         -e "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin" \
         $docker_hub cat /etc/os-release | grep "^ID=.*\n" | cut -d= -f 2 | xargs`
+fi
 
 if [ -z $distro ]; then
     echo "Cannot identified $docker_hub distribution" 1>&2
@@ -240,6 +242,7 @@ esac
 
 cat > $dockerfile <<EOC
 FROM $docker_hub
+USER root
 $commands
 RUN echo "#Generated by OpenNebula" > /etc/resolv.conf
 RUN rm -f /etc/ssh/ssh_host_* > /dev/null 2>&1