Refactored assertions for HAProxy monitoring
Refactored assertions for HAProxy monitoring

- Removed pre-condition assertions as they're handled by other cases.
- Made exit assertion more idiomatic

Signed-off-by: Tyler Schultz <6b7a73f4f7cffc2a148becd12890940350ddfa95@pivotal.io>

cloudfoundry-incubator/cf-tcp-router,cloudfoundry-incubator/cf-tcp-router