docker-compose: Upgrade from MariaDB 5.5 to MariaDB 10.3

NOTE: we're upgrading b/c all of the new migrations introduce
schema altering operations which fail on older versions of
MariaDB!

WARNING:

kiwi_db_data volume mount dir changed from `/var/lib/mysql' to
`/var/lib/mysql/data' b/c the latest version of MariaDB uses
a different datadir setting!

HOW TO UPGRADE:

WARNING: upgrade your database BEFORE upgrading to Kiwi TCMS 8.0 !!!

1) Backup existing database with:

   docker exec -it kiwi_db mysqldump -u kiwi -pYourPass kiwi > backup.sql

2) docker-compose down
3) docker volume rm kiwi_db_data

   will remove existing data volume b/c of incompatibilities between
   different MariaDB versions

4) docker-compose up

   will recreate data volume with missing data. e.g. manage.py showmigrations
   will tell you that 0 migrations have been applied.

5) Restore the data from backup:

   cat backup.sql | docker exec -u 0 -i kiwi_db /opt/rh/rh-mariadb103/root/usr/bin/mysql kiwi

   note: this connects to the database as the root user

6) Proceed to upgrade your Kiwi TCMS container !

docker-compose.yml

@@ -3,9 +3,9 @@ version: '2'
 services:
     db:
         container_name: kiwi_db
-        image: centos/mariadb
+        image: centos/mariadb-103-centos7
         volumes:
-            - db_data:/var/lib/mysql
+            - db_data:/var/lib/mysql/data
         restart: always
         environment:
             MYSQL_ROOT_PASSWORD: kiwi-1s-aw3s0m3