RFR: 8219149: ProcessTools.ProcessBuilder should print timing info for subprocesses

[Kim Barrett]

[I’m not completely sure where this RFR should be sent, but core-libs-dev
and hotspot-dev seems likely to get reasonable coverage of those who
might care.]

Please review this change to the test library to add some "logging"
output to tests that spawn a child process to perform the test and
then analyze that child's output.  We are seeing occasional timeouts
in such tests whose cause is hard to pin down.  It's not clear whether
the excess time is in the child or instead some problem in the testing
framework.  The new logging output provides timestamps for (1) the
start of output collection from the child, (2) the start of waiting
for the child to terminate, and (3) the child's termination.  This
should be enough to determine whether the child is taking too long,
and hint at where (e.g. termination or not).

CR:
https://bugs.openjdk.java.net/browse/JDK-8219149

Webrev:
http://cr.openjdk.java.net/~kbarrett/8219149/open.00/

Testing:
Local hs-tier1 and verified the expected logging output is present.
mach5 tier1-3 to ensure there aren't any "obvious" unexpected problems
caused by the new logging.  (It seems unlikely, but...)