The `--network` flag is parsed differently for `podman pod create`.
This causes confusion and problems for users. The extra parsing
logic ignored unsupported network options such as `none`,
`container:...` and `ns:...` and instead interpreted them as cni
network names.
Tests are added to ensure the correct errors are shown.
Signed-off-by: Paul Holzinger <paul.holzinger@web.de>