[11] Review request: 8199684: Update minumum boot JDK to jdk-9+181

[Kevin Rushforth]

Phil,

Please review the following:

https://bugs.openjdk.java.net/browse/JDK-8199684
http://cr.openjdk.java.net/~kcr/8199684/webrev.00/

This is long-overdue cleanup to bump the minimum boot JDK to JDK 9 GA, 
which I discovered while working on the gradle changes for separating FX 
bits (and which you recently reminded me of).

Note that we could consider bumping the minimum to JDK 10 GA some time 
after it ships next week, but that would require more discussion and a 
heads-up that it was coming, whereas this just corrects an oversight and 
won't affect any developers at all.

-- Kevin