Add VSTS status badge to readme

[zooba]

Adds VSTS badges to the readme to show the CI build status (not PR builds).

The backports will have different branches in the URLs, so that the badges will match the right branch's build and link to the correct logs.

[zooba]

Also, I know the icons are bland. I believe they're going to be customizable soon, but right now between fixed badges and limited ReST formatting there doesn't seem to be a way to put better labels on them :(

[bedevere-bot]

GH-8961 is a backport of this pull request to the 3.7 branch.

[bedevere-bot]

GH-8962 is a backport of this pull request to the 3.6 branch.

[Mariatta]

Ok so eventually these will be different icons right?

[Mariatta]

Adding these badges sounds good to me, but perhaps we merge this only after you have different icons for each badge.
Right now I think it will be confusing to people.

[zooba]

I'm torn on that point. The alt text has the right info, but apparently GitHub (or just the preview?) doesn't set the hover text to it.

Besides, these are only interesting when they fail, and then the first thing you do is click on it anyway. The Travis badge doesn't distinguish between the various builds it runs.

[Mariatta]

Yeah but at least there's only one travis build badge.

I imagine for a person going to python/cpython the first time, and seeing three badges that look the same, their first reaction is probably, "oh there's a bug in readme, lets go fix it", clicked the edit button, and "oh wait, nevermind."
After that they're probably going to file a bug and tell us to differentiate those somehow.

[zooba]

True. I'm planning to dig into the build definitions again at the sprints and may collapse them all into a single icon, but haven't decided yet.

I just got the timeline from the VSTS team on when label customization will come out (very soon - best I can say publicly - but I'm getting us fast-tracked :) ) and I know the URL changes to make. So I'll add those now, and as soon as we get the feature enabled the badges will change.

(To be clear - the text "Linux", "macOS", "Windows" in the label will replace the part that currently says "build", and there'll still be the little logo next to it.)

[zooba]

(Oh, and especially for you @Mariatta, I made sure they're testing putting emoji in the labels ;) )

[moswald]

The deployment has reached your account:

https://python.visualstudio.com/cpython/_apis/build/status/Linux-Buildbot?branchName=master&label=🐧Linux🐧

[Mariatta]

Badges look great! And emoji!
Thanks 🌮

[zooba]

Thanks Matt!