[examples/front-proxy] Sandbox for breaking max ejection percent

[brirams]

Motivation

OutlierDetection.MaxEjectionPercent bills itself as a mechanism that will limit the percent of a cluster that will be ejected due to outlier detection:

max_ejection_percent
The maximum % of an upstream cluster that can be ejected due to outlier detection. Defaults to 10%.

However, this branch demonstrates that it isn't being honored. It:

• sets up the default outlier detection config and two different cluster entries into service1 at the front-proxy level
• updates the service script to return 500s when a fail header is specified in requests
• script that starts up docker, issues good and bad requests, then prints out the outlier detection log to show that a host is ejected.

[brirams]

There's no real action item here beyond just spot checking that I'm not being silly -- putting this up for comment before opening PR with envoy folk

[brirams]

filed a corresponding envoy issue here: envoyproxy#3263