[kolla] using local package mirror for image builds

HI All, Using `kolla-build -b ubuntu` to build container images keeps timing out (well hanging for literal days) seemingly on package downloads from remote mirrors. I'm new to kolla and kolla-ansible so I may be misdiagnosing the cause of my current issue but we de have local ubuntu package mirros which would be faster in any case. Is there a way to specify using only a local package mirror? Thanks, -Jon