[50-52, MariaDB] fix "rake db:mysql" for MariaDB >= 10.1
[50-52, MariaDB] fix "rake db:mysql" for MariaDB >= 10.1

MariaDB 10.1+ insists on CREATE USER. Since "IF EXISTS" for CREATE/DROP
is only supported in more recent versions, just silently drop the user
before.

While at it, make the whole file a bit more readable.

bruceadams/activerecord-jdbc-adapter,kares/activerecord-jdbc-adapter,kares/activerecord-jdbc-adapter,jruby/activerecord-jdbc-adapter,bruceadams/activerecord-jdbc-adapter,bruceadams/activerecord-jdbc-adapter,jruby/activerecord-jdbc-adapter,kares/activerecord-jdbc-adapter,jruby/activerecord-jdbc-adapter