Island: Don't catch Exception in POST /api/island-mode

Flask automatically traps exceptions, returns a 500, and logs a stack
trace. Since Flask will automatically return a 500, we don't need to
duplicate the functionality. Since it prints a stack trace, it provides
more useful information than catching it did.

monkey/monkey_island/cc/resources/island_mode.py

@@ -26,5 +26,3 @@ class IslandMode(flask_restful.Resource):
             return make_response({}, 400)
         except ValueError:
             return make_response({}, 422)
-        except Exception:
-            return make_response({}, 500)