Fix timeouts and failure generation

[marcoeilers]

This PR makes three changes:

• It modifies checkSmoke to have an option to use the assert timeout (by default, none) instead of the check timeout.
• It modifies smoke checks whose failure would lead to a verification error to use the assert timeout instead (since we don't want verification failures due to timeouts unless the assert timeout is set).
• It moves the code that generates the error message in QP consumes until after the crucial assert, which is important to get the correct counterexample.

[jcp19]

LGTM