SA JMap - skip non-java thread stack dump for heap dump

when use SA JMap dump commands, such as "jhsdb jmap --binaryheap" or "dump heap" with "jhsdb clhsdb", it keep printing "dumpStack: not java Thread.".

This looks like an error/warning message, especially when the heap is large and the output prompts nothing but this message when heap dumping. As the heap dump only need to traverse the java thread, IMHO, it is better to skip dump non-java heap to avoid prompting this message.