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

[Schmelter, Ralf]

This change forwards the output from the HeapDumper.dump() command to an optional output stream supplied by the caller.
Until now the diagnositic command and the "dumpheap" command of the attach framework partly recreated the output by hand, but missing some information.

Old output:
Heap dump file created

New output:
Dumping heap to test.hprof ...
Heap dump file created [9719330384 bytes in 27,759 secs]

In addition to getting this improved information, it saves code too.

Bugreport: https://bugs.openjdk.java.net/browse/JDK-8233790 
Webrev: http://cr.openjdk.java.net/~rschmelter/webrevs/8233790/webrev.0/ 

Best regards,
Ralf