The 'redis' python module is required, 'pip install redis'

Hello,

I'm having the same problem as in [#12019](https://github.com/ansible/ansible/issues/12019) but with a newer version of ansible. I'm writing here as [@jimi-c](https://github.com/jimi-c) warns about people not reading comments to closed issues.

I have ansible 1.9.3 and redis but it doesn't work.

$ ansible --version                                         
ansible 1.9.3
  configured module search path = None
$ python -c "import redis ; print 'ok'"                                   
ok
$ ansible-playbook testset.yml --dry-run
The 'redis' python module is required, 'pip install redis'

Do you have any idea of how to proceed