CODETOOLS-7902093: IntelliJ plugin does not build against latest SDK

[Maurizio Cimadamore]

Hi,
please review the patch for fixing the jtreg build failures reported in 
this thread [1]. I also fixed few warnings, and took care of another 
build problem which has not been reported. Webrev here:

http://cr.openjdk.java.net/~mcimadamore/7902093/

[1] - 
http://mail.openjdk.java.net/pipermail/jtreg-dev/2017-November/000497.html

Thanks
Maurizio