RFR JDK-8031530: [TESTBUG] Enable test runtime/LoadClass/LoadClassNegative.java

[Zhengyu Gu]

The test was disabled due to JDK-8028095,  which is a dup of 
JDK-8020675. The problem has been fixed, this test should be re-enabled.

Bug: https://bugs.openjdk.java.net/browse/JDK-8031530
Webrev: http://cr.openjdk.java.net/~zgu/8031530/webrev.00/ 
<http://cr.openjdk.java.net/%7Ezgu/8031530/webrev.00/>

Thanks,

-Zhengyu