Fix EventBase death tests
Fix EventBase death tests

Summary:
Existing test was supposed to be testing the exception, but was instead dying because of the pid check.
Have 2 separate tests and use crash message regex to make sure they actually test what they are supposed to be testing.

Differential Revision: D24461683

fbshipit-source-id: b7ef30e488d266ea17e283f9b13b5d013a4a125a

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly