Allow aml_tester to report test outcome using DefFatal

[IsaacWoods]

DefFatal can be used by ASL to report a fatal error to OSPM. We can use this to test features of ASL within asl_tester.

• [ ] Don't panic, but mark test as failing, if DefFatal is encountered
• [ ] Allow annotation from test to signal that a DefFatal is expected, so we can test it
• [ ] Add a test for DefFatal to make sure it's parsed and handled correctly