The PR containers/podman#6442 enables a new way to create
shell completions scripts. The shell completion is handled
by cobra and since the login/logout flags are defined here
the completion functions for this should be defined here
as well. For Reference see:
https://github.com/spf13/cobra/blob/master/shell_completions.md
I added a unit test to ensure that the flags have a
completion function set.
This could also be used by skopeo and buildah if
someone wants to implement such completions for them.
Signed-off-by: Paul Holzinger <paul.holzinger@web.de>