Fix problems with Ansible playbook in vagrant

[wolfgang42]

• | failed was deprecated in Ansible 2.5 and removed in 2.9
• The python dpkg alternative doesn't seem to be available by default, but we're only interested in python3 anyway.

With these two changes, vagrant up now runs successfully with the latest version of ubuntu/xenial64 (v20210316.0.0) and Ansible 2.9 (which is not the latest version, just what I happen to have installed).