[WFLY-3883] use a LIST for the JMS connection-factory's connector attribute

and for the pooled-connection-factory too.

* for legacy versions, the LIST of STRING is converted to a MAP by the
  messaging transformers
* the attribute defines a value converter to ensure than legacy
  operations (that uses a MAP) can still be executed on the latest
  version.

JIRA: https://issues.jboss.org/browse/WFLY-3883