Remove MaxPermSize from server scripts when Java 9 is used

I'm not sure how easy this will be, but I think we need some way to do this.

Right now when you set up your WildFly 9 to use JDK 9, it will not start because MaxPermSize is no longer allowed as an argument.

The server will fail to start with this:

Unrecognized VM option 'MaxPermSize=256m'
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

In JBIDE-19049 we concluded that for now the workaround is to remove that parameter from Launch config manually if needed. This still works, but it would be best if we could somehow detect which version of Java is to be used and adjust the script accordingly. I know it can be tricky, especially when you use an exec env with the server and not a specific JVM directly.

One option would be to check for permgen support beforehand. But a problem I can see is that the exec env can change between server setup and server start, so we would need to check right before the start. Something like what they do here - via a script:
https://answers.atlassian.com/questions/17903656/java-warning-ignoring-option-maxpermsize
Maybe checking this at the time of server setup would still be better than nothing.