RFR 8218195: [testlibrary] Diagnostic output for test library ProcessTools

[Roger Riggs]

Please review the addition of diagnostic output to the test library 
ProcessTools.executeProcess
to aid in diagnosing several unexplained timeouts.

It adds a second check for process being aliev using ProcessHandle and 
prints
information about the current process and its descendents and all processes.

Webrev:
    http://cr.openjdk.java.net/~rriggs/webrev-pt-alive-patch-1/

Thanks, Roger