General improvements

[annismckenzie]

What was changed

This contains a few changes and fixes we made during our load testing journey:

• allow setting the TLS server name using the TLS_SERVER_NAME environment variable
• fix the name of the TLS_CLIENT_CERT_PRIVATE_KEY_File environment variable (should be all uppercase, probably a copy'n'paste mistake)
• nit: format Go code with go fmt which improves the general readability of the code

The biggest change in terms of lines was reducing the amount of logs produced. Without at least some changes Maru produces tens of thousands of lines of logs for even small and medium sized scenarios.

Why?

These changes make the project easier to work with when running a lot of scenarios on a regular basis.

Checklist

1. How was this tested:
   We ran extensive load tests using the updated version. We opened a fork-internal pull request for reference (Misc fixes alfatraining/maru#1) which isn't going to be merged and also contains a couple more changes we felt we shouldn't try to upstream.

2. Any docs updates needed?
   No, not yet. Some changes affect the Helm chart but that's not published and doesn't have any documentation.

[CLAassistant]

All committers have signed the CLA.