add readme file for edx-west, prod-log playbook

While in here do a couple of cleanups:

- remove a log file
- add a simple playbook for refreshing roles on the prod log machine
Add overview info and warning to west/README (per @jrbl)
Merge pull request #503 from edx/sef/west-readme-master

add readme file for edx-west, prod-log playbook (into master)