Add --use-colors cli option (second attempt)

[rsenseman]

resolves #2192

Description

New PR with same changes as #2622, I got myself into a Git-mess in PR #2622 when attempting to squash commits.

Adds two new flags --use-colors and --no-use-colors to dbt run command to enable or disable log colorization from the command line. The motivation for this change is to enable running with colorized logs locally and running without colorized logs in production for easier log parsing by other tools.

PR for documentation: dbt-labs/docs.getdbt.com#286

Checklist

• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have updated the CHANGELOG.md and added information about my change to the "dbt next" section.

Testing

Ran locally with all 4 combinations of profiles options use_colors: < true | false > and cli options nothing, --use-colors, and --no-use-colors to make sure overrides work as expected. Also added integrations tests to test that these flags work. Tests for both --use-colors and --no-use-colors implicitly test that default overrides are working.

Successfully ran integration tests with command docker-compose run test tox -e explicit-py36 -- -s -x -m profile_postgres test/integration/061_use_colors_tests/.

Also successfully ran make test-unit to make sure I didn't break anything already in place.

[jtcohen6]

LGTM! Thanks for opening a new PR. I did the same testing locally and all looks good.

If you can fix the changelog merge conflict, I'm happy with getting this in for our 0.18.0 release candidate.

[rsenseman]

@jtcohen6 Merge conflicts are resolved!

[jtcohen6]

Thank you for the contribution!