Merge pull request #87 from Ouranosinc/test-thredds-meta

# Overview

Adds general debugging utilities regarding notebook `test_thredds`

## Changes

- Adds variable overrides in `test_thredds` for local debugging. 
- Adds important documentation notes regarding possible error debugging leads for `test_thredds` (based on actual issues encountered). 

## Related Issue / Discussion

- Relates to bird-house/birdhouse-deploy#188 (comment)

Author: fmigneault