fix: [docker-host] restart docker only if necessary

precise/host/hooks/install.d/60-docker.sh

@@ -1,17 +1,26 @@
 #!/bin/bash
 
-
+need_restart=
 if ! type -p docker; then
     echo "Installing docker..."
     curl -sSL https://get.docker.io | sh
 fi
 
-version="$(apt-cache madison docker-ce | cut -f 2 -d \| | grep 17.06 | head -n 1 | xargs echo)"
+docker_version=17.06
+if ! [[ "$(docker --version)" == "Docker version $docker_version"* ]]; then
+    version="$(apt-cache madison docker-ce | cut -f 2 -d \| | grep "$docker_version" | head -n 1 | xargs echo)"
     ## DOWNGRADE to 17.xx because 18.xx do not support registry v1
     apt-get install -y --force-yes docker-ce="$version"
+    need_restart=true
+fi
+
 
 if ! egrep 'disable-legacy-registry' /lib/systemd/system/docker.service 2>/dev/null; then
     sed -ri 's/^(ExecStart=.*)$/\1 --disable-legacy-registry=false/g' /lib/systemd/system/docker.service
+    need_restart=true
 fi
+
+if [ "$need_restart" ]; then
     systemctl daemon-reload &&
         service docker restart
+fi