Fix failure in --no-dex2oat invocation of 425-invokesuper.

We had two issues:
- dexmerger is broken and sometimes produces invalid dex files,
  thus the test was always failing. b/18051191.
- The reason only no-dex2oat caught it is because it doesn't prebuild,
  and our scripts just do not report an error when the prebuild failed.

I also gave up trying to emit the dex2oat error output in the console.
I clearly don't speak bash.

Change-Id: I34c40902855452ea0f3e0d4733e4149c87236cfe