RFR: 8206322: ZGC: Incorrect license header in gtests

[Kim Barrett]

> On Jul 3, 2018, at 6:04 PM, Per Liden <per.liden at oracle.com> wrote:
> 
> When the ZGC gtests where open-sourced, the license header in these files were not updated accordingly.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8206322
> Webrev: http://cr.openjdk.java.net/~pliden/8206322/webrev.0
> 
> /Per

Looks good, and trivial.