use the container name as journal tag not id

Docker by default will use the container id as the journal tag when
logging into systemd-journal.
Using the container name makes easier to see which log belongs to which container.

roles/docker/files/daemon.json

@@ -1,3 +1,6 @@
 {
-    "log-driver": "journald"
+    "log-driver": "journald",
+    "log-opts": {
+        "tag": "{{.Name}}"
+    }
 }