Treat exceptions in init event handler as fatal and shut down locust …

…right away.

locust/main.py

@@ -544,6 +544,9 @@ def assign_equal_weights(environment, **kwargs):
     # Fire locust init event which can be used by end-users' code to run setup code that
     # need access to the Environment, Runner or WebUI.
     environment.events.init.fire(environment=environment, runner=runner, web_ui=web_ui)
+    if log.unhandled_greenlet_exception:
+        # treat exceptions in init handlers as fatal. They are already logged so no need to log anything more.
+        sys.exit(1)
 
     if web_ui:
         web_ui.start()