Update some tests and config to be more maintainable

[hasezoey]

Summary

This PR does:

• change from mocha.opts to mocha.yml because mocha stopped supporting the .opts format
• re-set the ANSI color for the SHARD warning (otherwise the next console log's / debug logs would also be in that color)
• change common.js's uris to be consistent across both uri and uri2 (before only uri would have the env applied)
• change common.js to have a extra value databases so that the databases for uri and uri2 can also be used for things like useDb instead of just the full uri's
• change many tests from static uri's to use common.js's uri and uri2
• change many tests from static database names to use common.js's databases array
• change many tests to unify database naming to what is available in common.js's databases array
• change model.populate.test.js to not create connections in the tests themself when not required (and use global instead)
• change model.populate.test.js to handle cleaning db2 outside of the tests themself

Note: some changes have been cherry-picked from #12262 to have them already applied (because i dont know how long that PR will be open for) and those changes were unrelated to the point of the mentioned PR

Note for the mocha opts change: i have not re-set the reporter to be dot but instead spec because this is way more readable (both in CI and locally)