Enhancement/checking deployments and testing

[caparker]

A few different things to review here

• In the lib/measurements.js file I added an error catcher for adapter errors
• Added a lib/request.js file that holds a flexible client wrapper for got, see the defra adapter for its use. More could be done here, for example, by fine tuning the retries.
• Tweaked the deployment scheduler to deal with the fact that it would not run a deployment of once source. This was because of the two different filtering methods we were using and so I removed the old one.
• Cleaned up the testing script (index.js) to allow for better local runs of both the fetcher and the scheduler. I added a deployments argument that forces the testing through the deployments path and a nofetch argument that skips the actual fetching part. This lets us isolate the scheduler a bit better for local testing and development.
• Changed the default timeout to 15sec instead of 60. Not sure if you want to keep that or not.