Configurable log level for Envoy Sidecar proxy

[christianang]

Summary

It would be helpful if the log level for Envoy was configurable for debuggability or potentially just set to info by default. Currently the log level for Envoy is set to critical (executor/transformer.go#L727).

Expected Result

When I set a bosh property to configure log level for envoy I want to be able to call cf logs my-app and see proxy logs.

Open to other ways of configuring the log level too if bosh property isn't the best way to do this.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/164557245

The labels on this github issue will be updated when the story is started.

[sunjayBhatia]

info level logs seem a bit verbose to change the default to, we do not want to pollute the application log stream with too much envoy output so that it becomes less usable. In addition, adding that default seems like it would add a lot more log content for every application once route-integrity is the default, which might not be ideal for the loggregator system. We are going to keep the default at critical but will expose a property to enable operators/CF developers to change the envoy log level to their liking. See https://www.pivotaltracker.com/story/show/164883000 to follow along with that