[8u] RFR 8266187: Memory leak in appendBootClassPath()

[Zhengyu Gu]

Backport this patch for parity with Oracle 8u331. It fixes a memory leak 
and risk is low,

Bug: https://bugs.openjdk.java.net/browse/JDK-8266187
Patch: 
https://github.com/openjdk/jdk/commit/aa90df6f51940a73f9aa078a32768855c8568034

The original patch does not apply cleanly. The conflict is copyright 
year line. Resolved manually.

8u webrev: http://cr.openjdk.java.net/~zgu/JDK-8266187-8u/webrev.00/

Thanks,

-Zhengyu