Pynio tests are being skipped on TravisCI

[jhamman]

Problem description

Currently on Travis, the Pynio tests are being skipped. The py27-cdat+iris+pynio is supposed to be running tests for each of these but it is not.

https://travis-ci.org/pydata/xarray/jobs/341426116#L2429-L2518

I can't look at this right now in depth but I'm wondering if this is related to #1531.

reported by @WeatherGod

[WeatherGod]

Zarr tests and pydap tests are also being skipped

[WeatherGod]

Looking through the travis logs, I do see that pynio is getting installed.

[jhamman]

Zarr should be getting skipped; we're waiting on a zarr's 2.2 release. Pydap may be getting skipped because it requires network access.