RFR: JDK-8217733 Minor RunTest fixes

[Alexandre (Shura) Iline]

Looks good.

Shura

> On Jan 24, 2019, at 6:46 AM, Magnus Ihse Bursie <magnus.ihse.bursie at oracle.com> wrote:
> 
> This patch covers some different minor cleanups that I accumulated after working on RunTest:
>  * Do not override JDK_IMAGE_DIR for jcov testing; instead introduce JDK_UNDER_TEST (to be really explicit about which JDK we're testing).
>  * Remove unconditional $(info) printout on Windows
>  * Group JCov variable setup with other variable setups.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8217733
> WebRev: http://cr.openjdk.java.net/~ihse/JDK-8217733-minor-RunTest-fixes/webrev.01
> 
> /Magnus