RFR[15] 8245151: jarsigner should not raise duplicate warnings on verification

[Hai-May Chao]

Hi,

I’d like to request a review for -

JBS: https://bugs.openjdk.java.net/browse/JDK-8245151
Webrev: https://cr.openjdk.java.net/~hchao/8245151/webrev.00/

The change is to provide a distinct warning for jarsigner -verify command when 
it detects weak timestamp digest algorithms are used (by -tsadigestalg when 
signing).

Thanks,
Hai-May