Compatibility issue with Java 9

[dariost]

Terasology crashes when trying to create a new game giving this error.
After discussing it with @Cervator on IRC he found out the crash is related to the Java version installed on my pc.

$ java -version
openjdk version "9"
OpenJDK Runtime Environment (build 9+181)
OpenJDK 64-Bit Server VM (build 9+181, mixed mode)

Java 9 is now in general availability and has already landed in the Arch Linux repository.

[dariost]

I should also add that there's a lot of flickering while Terasology is starting (I did a screen capture, ignore the flickering that happens after 0:12 because that is my iGPU which is not fast enough to record the screen and load the game)

[gianluca-nitti]

I think I found a (one-line) fix, see #3107 for more information.
If you want to test you should be able to do it with a git clone https://github.com/gianluca-nitti/Terasology && cd Terasology && git checkout java9-fix && ./gradlew game in a temp directory.

[dariost]

@gianluca-nitti running ./gradlew game gives an error (I added a --info for the log)

[dariost]

After discussing it with @gianluca-nitti he found out that the problem with gradle was because of the Arch Linux packaging; after having managed to get gradle to build Terasology I confirmed that Gianluca's PR fixes the problem with creating a new game (the graphical flickering and glitches remain)