script: indicate any error in test.bash

The test.bash script only indicated unknown tool errors in its exit status.
Other unexpected behavior has been considered warnings.  They were logged but
not indicated in the exit status.

Turn all warnings into errors.

Change-Id: I70f557459c4eef8e8ff8f655514b61511bdd0208
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>