cp: consolidate and simplify

[vrothberg]

Consolidate and simplify code in podman cp a bit. PR #11049
introduced some code duplicates that were worth tackling.

Signed-off-by: Valentin Rothberg [email protected]

[vrothberg]

Based on comments from @rhatdan

@containers/podman-maintainers PTAL

[openshift-ci]

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[rhatdan]

LGTM, Big improvement.

[infiniteregrets]

Thank you @vrothberg! Can you please update the manpage? I have made the changes, just add them to your commit if possible. If you want I can open a new PR to do that, but would be irrelevant I think.
https://gist.github.com/infiniteregrets/9b75f48c50dc0d060cf4aaf67d29cd8c (updated page with manpage syntax)

[vrothberg]

Thank you @vrothberg! Can you please update the manpage? I have made the changes, just add them to your commit if possible. If you want I can open a new PR to do that, but would be irrelevant I think.
https://gist.github.com/infiniteregrets/9b75f48c50dc0d060cf4aaf67d29cd8c (updated page with manpage syntax)

I updated the man page already in #11049. If you want more changes, please open a PR.

[vrothberg]

Green and ready to merge

[ashley-cui]

/lgtm