RFR: JDK-8230067: Add optional automatic retry when running jtreg tests

[Erik Joelsson]

For some notoriously unstable client tests, we need the ability to 
automatically retry them a few times. This can be achieved with a simple 
loop around running jtreg from RunTest.gmk and by using the 
-status:error,fail parameter on the retry runs. This parameter was fixed 
to actually work in this way in jtreg 4.2 b15.

Bug: https://bugs.openjdk.java.net/browse/JDK-8230067

Webrev: http://cr.openjdk.java.net/~erikj/8230067/webrev.01/index.html

/Erik