During cluster configuration, the hostname is getting resolved to IP,
as etcd requires IP address as listening address.
Due to connectivity flakes or delayed network inititalization, sometimes
the IP fails to be resolved to a name with following error:
```
[Errno -2] Name or service not known
```
that leads to attempt to run etcd with empty flag.
The PR adds a proper retry (up to 5 minutes) in case the connectivity
problems happens.
I considered alternatives like: `getent hosts foo`, but unfortunetelly thay
can return IPv6 that etcd is not ready for (yet).
de442ef860