Gateway passive health checks "status code 0" is not considered for ejection

Overview of the Issue

When the downstream service timeout to connect to the upstream (connection failure, timeout, TCP reset, etc.), Consul produces a "status code 0" to reflect this connectivity issue. Conceptually these events should be considered for gateway passive health checks ejections, but they are not.

• consul version: 2.0.2
• dataplane: 2.0.2
• consul-ecs: 0.10.0