Add HTTPS for build.servo.org

[jdm]

This is yolo-deployed so it can be observed to work: http://build.servo.org/grid should load https://build.servo.org/grid.

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This change is 

[jdm]

I originally had an HTTPS redirect for any HTTP URL, but that broke our tools like ./mach filter-intermittent that became confused by a 307 response. We'll need to do this in two stages - first, turn on HTTPS. Once we've migrated everything to use HTTPS URLs, we can add the HTTP->HTTPS redirect. This should be ready to merge and deploy in its current state.

[aneeshusa]

Thanks for working on this! I'd also love to see more software support 307s - if you have an error message handy I'd be interested in seeing what we can do about that.

[aneeshusa]

In the interest of being a good internet citizen, let's not use midnight directly but a more "random" time as the base - I'm sure they already get way too many requests right at midnight. Additionally, we can use sleep to add some more jitter: https://stackoverflow.com/questions/9049460/cron-jobs-and-random-times-within-given-hours/16289693#16289693 for example.

[aneeshusa]

Instead of running once a month, it would be nice to run once a week (ish) so we can catch problems faster. Also, we should figure out a story for getting notifications of failed jobs.

[jdm]

@aneeshusa servo/servo#20267 (comment)

[jdm]

I've addressed both comments. My best idea for notifying when the job fails is to file a github issue in this repository.

The requested changes have been completed.

[edunham]

Looks good to me. I agree that failures should report to somewhere, perhaps a GitHub issue, but I would rather not block landing this on setting that up.

@bors-servo r+

[bors-servo]

📌 Commit 9c60f7f has been approved by edunham

[jdm]

I mean, the changes in this PR include filing a github issue when there's a failure, so... :)

[bors-servo]

⌛ Testing commit 9c60f7f with merge cfdc53a...

[bors-servo]

☀️ Test successful - status-travis
Approved by: edunham
Pushing cfdc53a to master...