new TransactionManagerLocator class

[Thiago Veronezi]

Hi devs,
I've just uploaded a patch for a new feature. Please take your time to
review it and let me know if it is OK.
It would help me a lot with something that I plan to do with qpid.

https://issues.apache.org/jira/browse/QPID-5125

[]s,
Thiago.