RFR: 8213942:URLStreamHandler initialization race

[Seán Coffey]

A race condition recently reported by the WLS team. Access to the 
handlers Hashtable and the factory should be made while holding the 
streamHandlerLock lock.

WLS team also made efforts to create a reproducer. I've modified to 
jtreg format and reduced it down further for unit testing.

https://bugs.openjdk.java.net/browse/JDK-8213942
webrev: http://cr.openjdk.java.net/~coffeys/webrev.8213942/webrev/

regards,
Sean.