[BUILD] Support docker mirror in download script

A new option '--docker-private-registry-mirror' is added that allows
pulling images which originate from private registries from custom
docker mirroring repository (pull through cache)

Change-Id: I28ee693438d3684d3d0000a7dd94a265c0a617c1
Issue-ID: OOM-2915
Signed-off-by: Bartek Grzybowski <b.grzybowski@partner.samsung.com>
2 files changed