JBTM-622 : Support for crash recovery of tx-inflow with multiple resource managers

JCA tx-inflow spec allows the external EIS to provide the Xid for the inflowed transaction. The TM handling the inflowed (i.e. subordinate) transaction uses this Xid verbatim when talking to RMs.
In current implementation, each RM enlisted in the subordinate tx will see the same Xid as originally provided by the EIS. This screws recovery where multiple resources are involved, since a given Xid no longer belongs to exactly one RM, but may be shared by several. We can no longer return a single XAResource to drive the recovery for a given Xid.