RFR (XS) 8233790: Forward output from heap dumper to jcmd/jmap

[Schmelter, Ralf]

Hi Serguei,

Thanks for the review. The only open question seems to be:

> The dumper.dump() returns int value.
> Returned value is not used anymore in the attachListener.cpp and diagnisticCommand.cpp.
> Is it still used somewhere else or we can replace it with void?

The jmm_DumpHeap0 method still uses the return code (and the error string) to throw an
exception in case of an error.

Best regards,
Ralf