verify buildah/podman work before doing anything

[TomasTomecek]

Trying bender now in a funky environment and got this:

12:38:13.394 buildah_builder.py ERROR  couldn't locate python interpreter, tried these paths: ('/usr/bin/python3', '/usr/local/bin/python3', '/usr/bin/python2', '/usr/local/
bin/python2', '/usr/bin/python', '/usr/local/bin/python')                                                                                                                   
There was an error during execution: no python interpreter was found in the base image "registry.fedoraproject.org/fedora:29", you can specify the path via CLI option --pyth
on-interpreter       

The real problem:

12:38:34.753 utils.py          INFO   running command: "['podman', 'run', '--rm', 'registry.fedoraproject.org/fedora:29', 'ls', '/usr/local/bin/python']"
12:38:34.753 utils.py          DEBUG  podman run --rm registry.fedoraproject.org/fedora:29 ls /usr/local/bin/python
12:38:35.101 utils.py          DEBUG  container create failed: systemd cgroup flag passed, but systemd support for managing cgroups is not available
12:38:35.101 utils.py          DEBUG  : internal libpod error

Bender should report the original problem right away.
Also try to look for the python interpreter should fwd error logs.