"shell" step doesn't support check mode, which currently leads to failures,
when Ansible is being run in check mode (because Ansible doesn't run command,
assuming that command might have effect, and no "rc" or "output" is registered).
Setting "check_mode: no" allows to run those "shell" commands in check mode
(which is safe, because those shell commands doesn't have side effects).
A freshly-installed CoreOS system does not always have a hostname configured.
This causes problems for etcd and BGP mesh configuration for Calico.
Assign the Ansible inventory name as hostname as part of CoreOS bootstrap,
if the hostname is the default ("localhost").