This utility was only used in the CLI, but the implementation was
based on it being used on the daemon side, so included resolving
the host's IP-address, mirrors, etc.
The only reason it's used in the CLI is to provide credentials for
the registry that's being searched, so reduce it to just that.
There's more cleaning up to do in this area, so to make our lives
easier, it's implemented locally as non-exported functions; likely
to be replaced with something else.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
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