fix(artillery): update payload path when using environments

[bernardobridge]

What

Fixes #1961

How

This was happening because checkConfig gets called twice when you pass in a scenario + config. In that situation, if you have environments, the first time checkConfig gets called, it correctly creates the payload in the root config and replaces those paths.

However, it doesn't do the same to config.environments.payload. So the second time checkConfig is called, the _.merge overrides the payload path with the config.environment.payload unresolved path, causing the issue.

The PR addresses that by ensuring that it no longer gets called twice.

Testing

This was tested with the test scripts provided in the issue (very helpful), against Artillery Local.

Two things are missing:

• Verify this against non-local runs. This may still need to be accounted for, as I'm not sure if it uses the same logic, looking at create-bom.js;
• I am still in the process of figuring out a potential automated test for this.