test/py: exit(1) if there are problems running py.test

test/py: exit(1) if there are problems running py.test

The test/py/test.py wrapper script catches exceptions thrown when
exec()ing py.test in order to print a helpful error message. However,
the exception handling code squashes the exception and so the script
exits with a non-zero exit code, leading callers to believe that it
passed. Fix this.

Signed-off-by: Stephen Warren <swarren@nvidia.com>