RFE: improve tox setup to have multiple targets

[yazug]

it would be nice as a Dev

to be able to have multiple targets in tox.ini so I could only run linting or unittests

currently pipenv combined with single tox config setup is causing pain for me to try to run/verify/improve just the linting checks/code on new code I'm working on.

I ended up having a dev env and then cat the tox.ini and picked out the one or two lines I wanted to run and manually ran it. But with tox it should be as easy as "tox -e flake8" or something like that to only tests linting and not the unittests.

[yazug]

Low level RFE but it would be nice to be able to run tox -e flake8 .... or some other better name and have it use normal tox behavior of not regenerating env and running just the linting checks or the unittests. Primary focus for this is dev's usage.

[jguiditta]

I use 'make lint' for linting, 'make test' for testing in my current env, and 'make test-all' for running tox.

[fuzzball81]

@yazug I have added this issue to our project as a todo card. Please see the project tab from more information.