RFR: JDK-8027627 LOG=trace hardcodes value to bash

[Tim Bell]

Hello Magnus:

> This is an old but trivial bug that I want to fix.
>
> Dmitry Samersoff <dmitry.samersoff at oracle.com> discovered that 
> LOG=trace only works if bash is in /bin. He also suggested this patch.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8027627
> WebRev: 
> http://cr.openjdk.java.net/~ihse/JDK-8027627-dont-hardcode-bash/webrev.0

Looks good to me.

/Tim