Clear MariaDB dir after package install.

util/docker/mariadb/setup/mariadb.sh

@@ -15,6 +15,13 @@ apt-get update
 
 apt-get install -q -y --no-install-recommends mariadb-server mariadb-backup
 
+rm -rf /var/lib/mysql
+mkdir -p /var/lib/mysql /var/run/mysqld
+chown -R mysql:mysql /var/lib/mysql /var/run/mysqld
+
+# ensure that /var/run/mysqld (used for socket and lock files) is writable regardless of the UID our mysqld instance ends up having at runtime
+chmod 777 /var/run/mysqld
+
 # comment out a few problematic configuration values
 find /etc/mysql/ -name '*.cnf' -print0 \
   | xargs -0 grep -lZE '^(bind-address|log|user\s)' \