RFR: Add log message to clarify when the "Proactive" rule will be enabled again

[Erik Österlund]

Hi Per,

Looks good.

Thanks,
/Erik

On 2018-03-05 15:33, Per Liden wrote:
> It's sometimes non-obvious why the "Proactive" rule is disabled and 
> when it will be enabled again. This patch adds a log message to 
> clarify that.
>
> http://cr.openjdk.java.net/~pliden/zgc/print_proactive_disabled/webrev.0/
>
> /Per