Add dlint pre-commit and CI checks

[mssalvatore]

See additional_dependencies https://pre-commit.com/#pre-commit-configyaml---hooks

Tasks:

• As a follow up to Address Flake8 issues #1071, add dlint as an additional dependency for the flake8 pre-commit hook (test on pre-commit) (0d) - @shreyamalviya
• Add to travis. (0d) - @shreyamalviya
• Resolve all dlint issues:
  • DUO102 and DUO106 (0d) - @shreyamalviya
  • DUO116 use of "shell=True" is insecure in "subprocess" module (0d) - @shreyamalviya
  • Investigate and add NoQA to: DUO122 and DUO123 (0d) - @shreyamalviya
• Run blackbox tests (0d)