Best-effort attempt to check for remote maintenance

[lbonanomi]

Per #179 this change attempts to poll a remote instance to check its maintenance status and abort update-stats.py if the instance is currently under-maintenance.

Checks are executed with the (batteries-included) http.client and json libraries instead of Requests to enhance portability

[larsxschneider]

Thanks for opening this PR, @lbonanomi !

I think there is an easier way to query the maintenance status. Can you try to run this command via the admin SSH console?

ghe-maintenance --query

More info here: https://help.github.com/en/enterprise/admin/installation/command-line-utilities#ghe-maintenance

[lbonanomi]

@larsxschneider I agree that ghe-maintenance --query is simpler, it just seemed prudent to knock on the proverbial door before trying to log-in.

If you think calling on the maintenance API is the wrong thing to do may I try again with the CLI tools?

[larsxschneider]

I would prefer the CLI tools as we already have the SSH key to access the console nicely. Calling the maint API is not wrong, it is just that we would need to store additional credentials to access the API.

[lbonanomi]

Closing this PR to pivot the test-for-maintenance model, I'll be back after the weekend with a CLI-based check.