RFR(S): 8168483 Remove jtreg timeout handler timeout

[Staffan Larsen]

When we run jtreg in the hotspot, jdk and nashorn folders we run it with the timeout handler found under test/failure_handler. This handler is sometimes very slow (since it creates core files of hung processes). The handler is also very good at handling its own timeouts. 

The default implementation in jtreg tries to interrupt() a timeout handler after 300 seconds. This is not enough time for test/failure_handler. Rather than increasing the timeout, we should disable it when running with test/failure_handler and let it handle any timeouts itself.

webrev: http://cr.openjdk.java.net/~sla/8168483/webrev.00/
bug: https://bugs.openjdk.java.net/browse/JDK-8168483 <https://bugs.openjdk.java.net/browse/JDK-8168483>

/Staffan