Upgrade to python 3.5+ syntax, add autoformat

[alok]

Addresses #11749. If autoformat (done with black) is not desired, I can remove
that.

If it is desired, then I still need to add it to Travis to enforce that people
use it. One issue is that it requires 3.6+ to run.

[LucianaMarques]

Hi @alok ! My latest PR changed the iptestcontroller.py file, so you probably need to rebase your local repository.

[Carreau]

Thanks ! I'll try to have a look when I can !

I can remove that.

Well we'd love to enforce black, but we don't want to modify all the files at once as it would break some things like git blame; see among other this discussion and this thread on twitter; if you don't mind removing/rebasing that would be great.

[alok]

@Carreau I rebased. Though if you wouldn't mind updating the tests, that would be nice since I have no idea what the mini-language for test case formatting is.

[Carreau]

since I have no idea what the mini-language for test case formatting is.

Not quite sure what mini language you are referring to.
Also in #11749 I was referring to actuall checking of Python version like here, here ,

Ss this touch ~150 files, I might end up integrating it in multiple step. Did you use a script or changed all by hand ?

[alok]

Nevermind, it was an issue that came up with black.

I just ran pyupgrade --py3-plus **.py. That was it.

[drunkwcodes]

This PR may really break python2.7 compatibility in master such as string prefix u deletion.
Would you like to add a warning for python2 users pinning the version to 5?

And it is better to remain PEP461 string formatting unchanged for the target python version is 3.5.

[alok]

@drunkwcodes I'm not going to do any of that. 2.7 support has been dropped since 6.0, which came out 2 years ago.

[drunkwcodes]

@alok Fine. But PEP461 formatting?

[alok]

What is that

[drunkwcodes]

@alok That is the proof of unnecessity about the change of string formatting.
Reverting those changes and u prefix deletion makes this PR less possible to be rejected.