CLI does not fill NetworkAttachmentConfig.Target correctly

The CLI used to put whatever reference to a network the user entered directly into NetworkAttachmentConfig.Target. This field is documented to only contain a network ID, so this was the wrong behavior. It turned out that the daemon was automatically rewriting these names into IDs, which is bad because the daemon shouldn't be modifying the spec supplied by the user. The CLI behavior was fixed as part of https://github.com/moby/moby/pull/32062, and there was a lot of discussion about this in the PR:

https://github.com/moby/moby/pull/32062#discussion_r108245707
https://github.com/moby/moby/pull/32062#discussion_r110199017
https://github.com/moby/moby/pull/32062#issuecomment-292242071

The daemon still rewrites names into IDs for backward compatibility, but this code path isn't meant to be used going forward, and ideally should only be enabled for older API versions.

The CLI's behavior appears to have regressed in #62. It's no longer using the ID as it should. The problem is hidden by the magic rewriting in the daemon.

Read the behavior discussed in PR #32062 and the regression described in issue #62, then trace where the CLI constructs NetworkAttachmentConfig.Target. Confirm the CLI supplies a network ID rather than a name, and add or update coverage for that behavior if the relevant test location is found.