Add option to stop instance on Illegal Instruction error

[jairideout]

With several projects that are currently being tested with Clout (PyNAST, PyCogent, and QIIME), we occasionally get Illegal Instruction error messages. These occurrences are pretty rare, however, so it would be nice to have an option to stop the current instance if an Illegal Instruction error is encountered in any of the unit test log files. This would allow someone to manually investigate what is causing the issue and then terminate the instance.

[jairideout]

Stopping the instance won't help us here because the underlying hardware will most likely change once it is started again. After some internal discussion, we've decided to keep the instance running, and whenever Clout is run again, it will terminate any existing instances (so that we don't use too much money keeping an instance running that can't be tested within 24 hours). If the Illegal Instruction occurs on a weekend, the instance will be terminated as normal (as someone likely won't have time to test the instance over the weekend).