message: simplify with mkdir/fix-permissions.
  remove redundancy with mkdir -p
diff: @@ -18,10 +18,8 @@ ENV BACKUPS_DIR="/var/lib/mysql/backup"
  RUN apk add --no-cache bash mariadb-client mariadb mariadb-common pwgen && rm -rf /var/cache/apk/*
  -RUN set -xe; \
  - mkdir -p /var/run/mysqld /var/lib/mysql /etc/mysql /etc/mysql/conf.d /etc/mysql/ "${BACKUPS_DIR}"; \
  - chgrp -R root /var/run/mysqld /var/lib/mysql /etc/mysql /etc/mysql/conf.d /etc/mysql/ "${BACKUPS_DIR}"; \
  - chmod 770 /var/run/mysqld /var/lib/mysql /etc/mysql /etc/mysql/conf.d /etc/mysql/ "${BACKUPS_DIR}";
  +RUN for i in /var/run/mysqld /var/lib/mysql /etc/mysql/conf.d "${BACKUPS_DIR}"; \
  +do mkdir -p $i; /bin/fix-permissions $i; done
  # USER mysql
  