RFR: JDK-8219788: Configure recommends JDK 8

[Tim Bell]

Erik:

>  This patch changes the help text printed when the bootjdk is
> missing to "OpenJDK distributions are available at
> http://jdk.java.net/." and removes all the OS specific help texts for
> that particular dependency.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8219788
> <https://bugs.openjdk.java.net/browse/JDK-8219788?filter=36357>
>
> Webrev: http://cr.openjdk.java.net/~erikj/8219788/webrev.01/

Looks good.

Tim