os_provision.py: appease the latest flake8
os_provision.py: appease the latest flake8

The latest flake8 doesn't like "naked except" clauses. Since we don't
fix it to a specific version, I was surprised that didn't happen sooner.
Let's just please it so we can use Homu for merges.

Closes: #73
Approved by: cevich

jlebon/redhat-ci,jlebon/redhat-ci