[refactor] simplify test_helper connection closing
[refactor] simplify test_helper connection closing

Also ActiveRecord::Base.connection gives an active connection which
might not be the one that is connected

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