`hostctl sync docker` doesn’t skip containers that do not have an IP address assigned

[lenormf]

Describe the bug
A clear and concise description of what the bug is.

Running hostctl sync docker … will add an entry to the hosts file that contains <nil> for IP address of all containers that do not have one assigned.

To Reproduce
Steps to reproduce the behavior:

1. Create a named container that does not have any network addresses assigned.
2. Run hostctl sync docker <profile>
3. The hosts file will contain an entry <nil> container.loc

Expected behavior
A clear and concise description of what you expected to happen.

A warning should be printed on the standard output that the named container does not have any IP addresses assigned, and no associated entry will be added to the hosts file.

Screenshots
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System (please complete the following information):

• OS: Ubuntu Focal
• Version: v20.04