Added unit test for ERRAI-672
Added `-out` parameter to Errai's JUnitShell

`-out` is a deprecated but valid argument for GWT's JUnitShell. Applications which
use `-out` failed with `Unknown argument: -out` when `errai-weld-integration` is
on the classpath.

For reference: GWT 2.5.1 JUnitShell
https://github.com/gwtproject/gwt/blob/2.5.1/user/src/com/google/gwt/junit/JUnitShell.java#L167
No longer printing gen. code to stdout (not needed: gen. code is written to files in .errai)
Ensured to never generate the cache/debug files in .errai more than once