Environment variable to enable debug logging

**Is your feature request related to a problem? Please describe.**
Right now when things go wrong, I have to hack any number of deploy scripts to add the `--debug` switch to `aws` commands.

**Describe the solution you'd like**
It would be much better to set `AWS_DEBUG` in the environment passed to these deploy scripts.

**Describe alternatives you've considered**
There are none.

**Additional context**
Bonus points for a syntax like `AWS_DEBUG='botocore.credentials botocore.utils'` etc.