Stop using dist-git lookaside cache for Porta productized build

The current Porta productized build relies on the dist-git lookaside cache (a place in dist-git where we can store source archives), for storing the node-headers archive, used here: http://pkgs.devel.redhat.com/cgit/containers/3scale-amp-system/tree/Dockerfile?h=3scale-mas-rhel-7#n34 

The archive is necessary because node-gyp otherwise tries to download the headers archive from the internet and the productized build would fail (there is no access to the internet allowed during productized builds). 

This has been working fine until today because the dist-git lookaside cache is a perfectly valid place to store such archives. However, as part of onboarding onto CPaaS Midstream, we need to move away from the lookaside cache, as CPaaS Midstream doesn't support it. 

(Note: this is actually an improvement, as the dist-git lookaside cache doesn't offer a very good mechanism to track the upstream source code origins of an archive that has been stored in it)