[HORNETQ-1230] fix compliance of RA getXAResources

fix HornetQResourceAdapter.getXAResources() by returning null (instead
of raising an exception) when auto recovery is used.
If there is no auto recovery, return the XAResources for each RA's
inflow activation endpoint.
Merge pull request #1162 from jmesnil/HORNETQ-1230_RA_getXAResources

[HORNETQ-1230] fix compliance of RA getXAResources