Just looking at the Man page for the mirror-locally option on cobbler repo add. Normally I would think that if I set --mirror-locally=true, then cobbler will mirror the repo locally and use the local mirror, but the docs seem to indicate the reverse:
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mirror-locally
When true, specifies that this yum repo is to be referenced directly via kickstarts and not mirrored locally on the cobbler server.
Only http:// and ftp:// mirror urls are supported when using --mirror-locally=1.