RFR(S): 8017510: Add a regression test for 8005956

[Niclas Adlertz]

Hi all. 

A regression test for 8005956 is needed. 
It's based on https://jbs.oracle.com/bugs/secure/attachment/11386/PolynomialRoot.java, which relates to JDK-8005956 (https://jbs.oracle.com/bugs/browse/JDK-8005956)

WEBREV: http://cr.openjdk.java.net/~adlertz/JDK-8017510/webrev00/
JBS: https://jbs.oracle.com/bugs/browse/JDK-8017510

Kind Regards,
Niclas Adlertz