[derby] allow to configure whether :transaction_isolation will be 'serializable'
[derby] allow to configure whether :transaction_isolation will be 'serializable'

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