backend/repository2: set auth headers for getLayer
backend/repository2: set auth headers for getLayer

It was causing authenticated docker fetches to fail.

jsoriano/docker2aci,OMWAVE/docker2aci,jonboulle/docker2aci,OMWAVE/docker2aci,appc/docker2aci,dgonyeo/docker2aci,vishvananda/docker2aci,dgonyeo/docker2aci,iaguis/docker2aci,appc/docker2aci,jsoriano/docker2aci,vishvananda/docker2aci