Updates sentry.conf.py for changes in env vars

I just tried this project, and I found that some of the environmental vars are not consistent with what Openshift gives you if you install it today.

There was one where I had to make a judgement call. There now seem to be two LOG_DIRs:

OPENSHIFT_MYSQL_DB_LOG_DIR
OPENSHIFT_DIY_DB_LOG_DIR

I chose DIY since it seems to be the more general. Let me know, I can change it to the MYSQL one if you'd like and resubmit the request.