RFR(xs): 8159019: ResourceMark in ClassLoader::open_versioned_entry() is being used incorrectly

[Calvin Cheung]

Please review this small fix for correcting the use of ResourceMark in 
classLoader.cpp.

bug: https://bugs.openjdk.java.net/browse/JDK-8159019
webrev: http://cr.openjdk.java.net/~ccheung/8159019/webrev.00/

Tested manually with the affected testcase on linux_x64.
Running tests on all platforms.

thanks,
Calvin