new: [docker-host] don't restart docker for certificate installation if it is not needed.

precise/host/hooks/install.d/70-0k.sh

@@ -162,16 +162,30 @@ apt-get install -y curl </dev/null
 
 
 ## This does not seem to work anymore (docker v1.12, ubutnu 14.04 on gani)
+ca=/etc/ssl/ca.0k.io.pem
+need_restart=
+oldmd5=
+if [ -f "$ca" ]; then
+    oldmd5=$(md5sum "$ca")
+fi
 echo "Fetching 0k.io CA certificate..."
-curl http://docker.0k.io/get/ca.0k.io.pem > /etc/ssl/ca.0k.io.pem
-cat /etc/ssl/ca.0k.io.pem >> /etc/ssl/certs/ca-certificates.crt
+curl http://docker.0k.io/get/ca.0k.io.pem > "$ca"
+if [[ "$(md5sum "$ca")" != "$oldmd5" ]]; then
+    need_restart=1
+    cat "$ca" >> /etc/ssl/certs/ca-certificates.crt
+fi
 
 ## This is the new way: https://docs.docker.com/engine/security/certificates/
-mkdir -p /etc/docker/certs.d/docker.0k.io
-ln -sfn /etc/ssl/ca.0k.io.pem /etc/docker/certs.d/docker.0k.io/ca.crt
-
+ca_ln="/etc/docker/certs.d/docker.0k.io/ca.crt"
+mkdir -p "$(dirname "$ca_ln")"
+if ! [ -L "$ca_ln" ] || [ "$(realpath "$ca_ln")" != "$ca" ] ; then
+    ln -sfn "$ca" "$ca_ln"
+    need_restart=1
+fi
 
-service docker restart
+if [ "$need_restart" ]; then
+    service docker restart
+fi
 
 echo "Login into our server."
 docker login -u vm -p iamavm https://docker.0k.io