Add OpenDAP backend

[jreadey]

Would it be worthwhile to add an OpenDAP server (e.g. Hyrax) as a backend data provider? Note: xarray supports OpenDAP: http://xarray.pydata.org/en/stable/io.html#opendap. Hyrax is used heaving in NASA data centers, so I imagine they will have some interest in how Hyrax compares with other storage methods.

[rabernat]

The challenge would be how to deploy the test Hyrax server. Results would obviously be quite dependent on the server and network performance. Ideally we could deploy in the cloud next to wherever the tests are running.

pydap is a lightweight, python alternative that could be easier to deploy programmatically: http://pydap.readthedocs.io/en/latest/