[EJBCLIENT-120] Hang in AbstractHandleableCloseable.close() when using @Clustered

Extract the logic from cluster context outside EJBClientContext for
uncoupling the operations between EJBClientContext and
ClusterContext. This removes the deadlock when both types
of operations are being invoked through the EJBClientContext.
BZ 6.x https://bugzilla.redhat.com/show_bug.cgi?id=1133980
I really am not happy with increasing the API surface area with another special-purpose class.  Is there a reason it has to be public?