Doc build on Azure is timing out on master

[shoyer]

I don't know what's going on, but it currently times out after 1 hour:
https://dev.azure.com/xarray/xarray/_build/results?buildId=2767&view=logs&j=7e620c85-24a8-5ffa-8b1f-642bc9b1fc36&t=68484831-0a19-5145-bfe9-6309e5f7691d

Is it possible to login to Azure to debug this stuff?

[shoyer]

I forgot that we use exactly the same doc build configuration on RTD, and I was able to get a traceback from there: https://readthedocs.org/projects/xray/builds/10969146/

It's too bad that we don't see that on Azure. Maybe there are some flags to edit in our invocation of sphinx.