Improve the docs of IBM MQ RA integration.

In the messaging book, the IBM MQ RA integration is very vague about how to enable XA Recovery. It only points to the XA Recovery chapter in EAP docs, which doesn't discuss about XA Recovery for RA, like IBM MQ. 

I'm not sure if both chapters should be improved, but I create a KCS that could be used as source to improve the documentation: https://access.redhat.com/solutions/7014035

Notice that IBM MQ RA configuration uses the old security subsystem. The KCS that I wrote uses the Elytron subsystem.