RFR (XS): 8007776: Test6852078.java timeouts

[David Chase]

http://cr.openjdk.java.net/~drchase/8007776/webrev.00/

Bug: Test6852078.java contained a 2000-test-iteration loop for tickling a sometimes-bug,
that also sometimes timed out after as few as 130 iterations on some slower machines.

Fix: Inserted an early-out on the test-loop -- if more than 100 seconds and more than
100 iterations have both passed, then exit is allowed. 
2000 iterations are still the norm on faster machines (e.g., on a modern Intel laptop it
takes 5 seconds to run).

Testing:
Jtreg, JPRT on that test.
Hand-tested the early-out logic by bumping the iteration count to 2 million; it exited after
a total test execution time of 100.5 seconds.