Cope with parameter name change due to SPR-9985

SPR-9985 means that, by default, parameter names in MBeanInfos will no
longer be named p1, p2, etc but, instead, will use names discovered
in the local variable table. This means that
OperationInvokingMessageHandler's approach of using a Map keyed by
p1, p2, etc no longer works.

OperationInvokingMessageHandler has been updated to instead, use a
Map, looking up the parameters by name, when the message's payload is
a map, and to use a list, looking up the parameters by index, when
the message's payload is a list.