RFR(s): 8243451: nsk.share.jdi.Debugee.isJFR_active() is incorrect and corresponsing logic seems to be broken

[Fairoz Matte]

Hi,

Please review this small test infra change to identify at runtime the JFR is 
active or not.

JBS - https://bugs.openjdk.java.net/browse/JDK-8243451
Webrev - http://cr.openjdk.java.net/~fmatte/8243451/webrev.00/

Thanks,
Fairoz