RFR 8210395: Add doc to SecurityTools.java

[Weijun Wang]

Ping again.

> On Sep 5, 2018, at 12:17 PM, Weijun Wang <weijun.wang at oracle.com> wrote:
> 
> I ran javadoc on test/lib so I can learn the useful helper classes, and find out SecurityTools.java has no javadoc at all.
> 
> Please review this change
> 
>   http://cr.openjdk.java.net/~weijun/8210395/webrev.00/
> 
> Thanks
> Max
>