Restore nightly CI builds

[yzdocs]

Fixes #8094.

See example of successful nightly build run here: https://teamcity.cockroachdb.com/buildConfiguration/Internal_Docs_Nightly/2428145?showLog=2428145_7378__expandAll

"Successful" as in htmltest checks return valid results. There is a known issue with 429 errors to GitHub (too many requests): wjdp/htmltest#152. For a quick fix, we could opt out GitHub links from being checked for now to cut down on noise.

Meanwhile, there are a bunch of 404 errors that are valid for fixing. Examples:

Non-OK status: 404 --- docs/v1.0/deploy-cockroachdb-on-microsoft-azure.html --> https://docs.microsoft.com/en-us/azure/virtual-machines/virtual-machines-linux-mac-create-ssh-keys

11:17:33
Non-OK status: 404 --- docs/v1.0/deploy-cockroachdb-on-microsoft-azure.html --> https://docs.microsoft.com/en-us/azure/virtual-machines/virtual-machines-linux-quick-create-portal
11:17:33
docs/v1.0/deploy-cockroachdb-on-microsoft-azure-insecure.html
11:17:33
Non-OK status: 404 --- docs/v1.0/deploy-cockroachdb-on-microsoft-azure-insecure.html --> https://docs.microsoft.com/en-us/azure/virtual-machines/virtual-machines-linux-mac-create-ssh-keys
11:17:33
Non-OK status: 404 --- docs/v1.0/deploy-cockroachdb-on-microsoft-azure-insecure.html --> https://docs.microsoft.com/en-us/azure/virtual-machines/virtual-machines-linux-quick-create-portal

Non-OK status: 403 --- docs/v1.0/frequently-asked-questions.html --> http://research.microsoft.com/en-us/um/people/lamport/pubs/paxos-simple.pdf
11:17:34
docs/v1.0/high-availability.html
11:17:34
Non-OK status: 403 --- docs/v1.0/high-availability.html --> http://research.microsoft.com/en-us/um/people/lamport/pubs/paxos-simple.pdf
11:17:34
docs/v1.1/orchestrate-cockroachdb-with-mesosphere-insecure.html
11:17:34
Non-OK status: 404 --- docs/v1.1/orchestrate-cockroachdb-with-mesosphere-insecure.html --> https://docs.mesosphere.com/1.9/security/ent/service-auth/custom-service-auth/
11:17:34
Non-OK status: 404 --- docs/v1.1/orchestrate-cockroachdb-with-mesosphere-insecure.html --> https://docs.mesosphere.com/1.10/installing/oss/cloud/aws/basic/
11:17:34
Non-OK status: 404 --- docs/v1.1/orchestrate-cockroachdb-with-mesosphere-insecure.html --> https://docs.mesosphere.com/1.10/installing/oss/
11:17:34
Non-OK status: 404 --- docs/v1.1/orchestrate-cockroachdb-with-mesosphere-insecure.html --> https://docs.mesosphere.com/1.10/installing/ent/
11:17:34
Non-OK status: 404 --- docs/v1.1/orchestrate-cockroachdb-with-mesosphere-insecure.html --> https://docs.mesosphere.com/1.10/installing/oss/cloud/aws/basic/#launch-dcos
11:17:34
Non-OK status: 404 --- docs/v1.1/orchestrate-cockroachdb-with-mesosphere-insecure.html --> https://docs.mesosphere.com/1.10/cli/install/
11:17:34
Non-OK status: 404 --- docs/v1.1/orchestrate-cockroachdb-with-mesosphere-insecure.html --> https://docs.mesosphere.com/1.10/deploying-services/install/#installing-a-service-using-the-gui

[cockroach-teamcity]

This change is 

[yzdocs]

Example of nightly run that skips checking GitHub links for now: https://teamcity.cockroachdb.com/buildConfiguration/Internal_Docs_Nightly/2428214?buildTab=log&expandAll=true&focusLine=111

We can look into checking GitHub links again once we clean up all the valid 404 etc errors. Does that sound good?

[jseldess]

Thank you, @yingzhuchin!

It would be amazing if we could auto-create a GH issue in our repo when this nightly test fails. Could we put that on the backlog?

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @jseldess and @lnhsingh)

[yzdocs]

It would be amazing if we could auto-create a GH issue in our repo when this nightly test fails. Could we put that on the backlog?

Yes, for sure: #8862. I'd like to implement it only after we've cleaned up the existing broken links though. Otherwise we might get a new GitHub issue every night!