Codes B301-B306 conflict with flake8-bugbear

This is related to a discussion ongoing in the flake8-bugbear repo issues: https://github.com/PyCQA/flake8-bugbear

Main points pasted below from @myii on Github:

```
The conflict is not with flake8-bandit but rather with openstack/bandit

There are two projects that are involved here:

    https://github.com/openstack/bandit
        Project started on 16 July 2014
        This is the main project, where the conflicts are arising

    https://github.com/tylerwince/flake8-bandit
        Project started on 29 Oct 2017
        However, this is just a wrapper around bandit
        They have no control over the error codes that are supplied by bandit

The OpenStack Bandit project has been using B30x codes for a few years as well

Taking B301 as the earliest example in both projects:

    Bandit: openstack/bandit@c364408
        This commit was made on 22 Jan 2016

    Bugbear: 0fb7d8d
        This commit was made on 8 Jun 2016
```