mc: compute default MOTD based on the given type and version

minecraft-server/start-finalSetup04ServerProperties

@@ -34,6 +34,22 @@ if [ ! -e $SERVER_PROPERTIES ]; then
     setServerProp "white-list" "true"
   fi
 
+  # If not provided, generate a reasonable default message-of-the-day,
+  # which shows up in the server listing in the client
+  if [ -z $MOTD ]; then
+    # snapshot is the odd case where we have to look at version to identify that label
+    if [[ ${ORIGINAL_TYPE} == "VANILLA" && ${VERSION} == "SNAPSHOT" ]]; then
+      label=SNAPSHOT
+    else
+      label=${ORIGINAL_TYPE}
+    fi
+
+    # Convert label to title-case
+    label=${label,,}
+    label=${label^}
+    MOTD="A ${label} Minecraft Server powered by Docker"
+  fi
+
   setServerProp "server-port" "$SERVER_PORT"
   setServerProp "motd" "$MOTD"
   setServerProp "allow-nether" "$ALLOW_NETHER"