[9-jake] review request: 8090171: Switch production build of FX to gradle 2.9

[Kevin Rushforth]

David,

Please review the simple change to the version check logic to use 2.9 as 
the preferred version of gradle (with 1.8 still being the default).

https://bugs.openjdk.java.net/browse/JDK-8090171
http://cr.openjdk.java.net/~kcr/8090171/webrev.00/

NOTE: as stated in my "HEADS-UP" e-mail, this will be pushed to 
sandbox-9-jake first and later to 9-dev

-- Kevin