Is your feature request related to a problem? Please describe.
Currently, constants.py defines some standard excludes hardcoded in a file. While this hasn't generally been an issue thus far, it does get complicated if someone wishes to override those values.

Describe the solution you'd like
Rather than hardcode in Bandit source, make use of a project's defined .gitignore file instead. It's very common to only scan the source that is part of the git repo anyway.

Describe alternatives you've considered
This solution would apply only to Git source control. So if someone uses SVN, CVS, etc, it may not be of much help.

Additional context
https://git-scm.com/docs/gitignore
https://github.com/PyCQA/bandit/blob/7fbf9d517b900936ac97e7debbd16dc7e532bc27/bandit/core/constants.py