add a more flexible case insensitive match to CI branch checks

[jshimko]

This adds a slightly more flexible check for branch names in the CI Docker build script. It will now trigger a Docker build/test on the following branches:

- master
- development
- *docker* (case insensitive regex)
- *release* (case insensitive regex)

The motivation for this update was to include "release" branches since they get merged straight to master and could potentially not have a recent Docker build test.