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

[Per Liden]

Thanks for reviewing!

/Per

On 03/06/2018 12:58 PM, Stefan Karlsson wrote:
> Looks good.
> 
> StefanK
> 
> 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
> 
>