scripts/install script forces use of ./venv virtualenv, impossible to use with virtualenvwrapper

[forsberg]

Checklist

• [X] I have included information about relevant versions
• [X] I have verified that the issue persists when using the master branch of Faust.

Steps to reproduce

Check out faust-streaming 40237bee24b310a6141b78059a363b85681a3c94, then

./scripts/install
./scripts/lint
./scripts/tests
<runs a lot of tests>
scripts/coverage: 11: codecov: not found

I'm not familiar with codecov, but I guess it should be run only if the environment variable CODECOV_TOKEN is set?

[forsberg]

It seems codecov is installed in the virtualenv venv, but I'm using virtualenvwrapper to create and switch between virtualenvs, and this seems unsupported by the install script.