Twisted's tox file should support specifying the different reactors

[hawkowl]

Right now it's just py27-tests or whatever -- it should be something like py27-tests-epoll and such (using the "platform" key to disable them on platforms), IDEALLY -- but it looks like that due to tox limitations, it'll have to be an environment variable, or we duplicate the trial command with each of the settings, for both -tests and -coverage (which isn't great).

I think the environment variable is the best right now, to make tox usable on the buildbots.

[hawkowl]

(In [47133]) Branching to tox-reactors-8269.

[hawkowl]

This adds it as a environment variable -- TWISTED_REACTOR in the environment is given to the --reactor trial flag.

Builders spun, please review.

[Adi Roiban]

I think that if you are happy with this, we should merge it.

Are the developers supposed to run the same tox file and set the TWISTED_REACTOR env var to run some tests? If yes, is this documented?

... even if this is not documented, I hope that this is just a transition phase and in the end we will have all logic for building and running tests encapsulated in the repo.

right now, the other part of this change is in twisted-infra/braid ...and there it can be merged without review... so I would say that since this is devtools part of twisted, we should also merge it without review.

thanks!

[hawkowl]

(In [47181]) Merge tox-reactors-8269: Add the ability to test specific reactors using the tox config

Author: hawkowl Reviewer: adiroiban Fixes: #8269