ansible: Add tag to python interpreter var setting tasks

ansible: Add tag to python interpreter var setting tasks

I'm working on a combination of terraform and ansible to quickly
spin up instances in IBM Cloud so they can join Jenkins as builders.

Part of this process involves creating a virtualenv and running ansible
from it.  python-jenkins needs to be installed in the virtualenv and
setting the python interpreters inside the playbook breaks that.

This PR will let me `--skip-tags interpreter`

Signed-off-by: David Galloway <david.galloway@ibm.com>