Test invalid submissions are safely discarded

[spbnick]

We just hit the same problem again with submissions: invalid I/O messages block the whole submission queue, because the kcidb_load_queue function throws an exception trying to load invalid data into the database. This shouldn't happen, and is being fixed, but we need a test that will prevent this from happening again.

The test should submit a message failing validation to the submission queue, followed (after a delay) by valid messages. The invalid message shouldn't make it, but the valid messages should.