python3 readiness

Currently if I try to have a CentOS8 ephemeral slave curl the setup script from prado (even with a symlink from `/usr/bin/python` to `/usr/bin/python3`), the playbook fails:

```
[ 67.169869] cloud-init[1814]: --> do not requiretty for sudoers
[ 67.172775] cloud-init[1814]: --> getting ready to fetch ansible
[ 93.910266] cloud-init[1814]: tar: main.yml: time stamp 2019-12-19 15:41:30 is 226.855353188 s in the future
[ 94.057665] cloud-init[1814]: Traceback (most recent call last):
[ 94.057916] cloud-init[1814]: File "/prado_1576787836/playbook/../build/bin/../ansible/bin/ansible-playbook", line 60, in
[ 94.058450] cloud-init[1814]: import ansible.constants as C
[ 94.058986] cloud-init[1814]: File "/prado_1576787836/build/ansible/lib/ansible/constants.py", line 19, in
[ 94.059511] cloud-init[1814]: from ansible.config.manager import ConfigManager, ensure_type, get_ini_config_value
[ 94.060358] cloud-init[1814]: File "/prado_1576787836/build/ansible/lib/ansible/config/manager.py", line 17, in
[ 94.060892] cloud-init[1814]: from yaml import load as yaml_load
[ 94.061492] cloud-init[1814]: File "/prado_1576787836/build/ansible/lib/yaml/__init__.py", line 2, in
[ 94.062070] cloud-init[1814]: from error import *
[ 94.062583] cloud-init[1814]: ModuleNotFoundError: No module named 'error'
ci-info: ++++++++Authorized keys from /home/cloud-user/.ssh/authorized_keys for user cloud-user+++++++++
```