CI: increase Ansible Galaxy retries & add delay

We still see flakiness when downloading content from Ansible Galaxy,
often HTTP 520. This change increases the retries from 3 to 10, and adds
a 5 second delay between attempts.

Change-Id: I0c46e5fcc6979027dc6f1bc5cc49e923a205f654
Related: https://github.com/ansible/galaxy/issues/2429