"acbuild copy" does not preserve file capabilities (setcap)

[alban]

Steps:

• use "setcap cap_ipc_lock=+ep" on the executable
• add it to the ACI with "acbuild copy"
• the file capabilities are not preserved

Workaround: untar & recreate the ACI using bsdtar manually.

Should "acbuild copy" just preserve the file caps or should an option be added for that?

Issue first reported in a stackoverflow question.

[cgonyeo]

I think it would make sense for it to preserve file caps. The copying is done by github.com/coreos/rkt/pkg/fileutil, so any changes will need to be made there.