s2i with buildah support

HI,

@otaviof I have seen this PR https://github.com/openshift/source-to-image/pull/1003, where this feature is being implemented and just want to check, so once this PR is merged and if I switch to use buildah as my container manager then the issue that am facing here will also be resolved ?#1016, the issue that am facing in 1016 is, the s2i containers that are getting spawned are repeatedly getting killed on Kubernetes when the Nodes are under memory pressure and am not able to figure out how to avoid them getting killed .

Am assuming with this implementation i.e through buildah in place the entire logic to build a container will execute within the same pod that has triggered the build using s2i, so that the memory and cpu limits that are applicable on POD will be applicable for the s2i build as well since the build will be running inside the pod

Start by reading PR #1003 and issue #1016, then compare their implementation and discussion with the memory-pressure behavior described here. Determine whether Buildah support keeps the build within the invoking Kubernetes pod and whether that makes its resource limits govern the build; the issue is done when this relationship is confirmed or the remaining changes are identified.