Install bandit on the build

### Motivation
[Bandit](https://wiki.openstack.org/wiki/Security/Projects/Bandit) is a n OpenStack project aimed at statically analyzing Python files for common security vulnerabilities. This PR installs the `bandit` package as a test dependency and as a build checker, as suggested by @hoffmabc.

### Changelog
* Install `bandit` as test dependency.
* Copy the default configuration file (`bandit.yaml`) from the OpenStack project.
* Write a simple script to integrate `bandit` with the build.

### Note
I couldn't find `bandit` at PyPI, so I opted to install it from the GitHub repo. The package is under active development, so I am not considering the errors it reports as build errors. This doesn't mean we shouldn't take them into consideration.