RFR 8222100: tools/jimage/JImageTest.java time out

[sundararajan . athijegannathan]

Bumping the default timeout (other tests in the same dir have similar 
timeout settings).

Bug: https://bugs.openjdk.java.net/browse/JDK-8222100
Webrev: http://cr.openjdk.java.net/~sundar/8222100/webrev.00/

Thanks,

-Sundar