Podman and Buildah should use the same code the generate the resolv.conf
file. This mostly moved the podman code into c/common and created a
better API for it so buildah can use it as well.
[NO NEW TESTS NEEDED] All existing tests should continue to pass.
Fixes#13599 (There is no way to test this in CI without breaking the
hosts resolv.conf)
Signed-off-by: Paul Holzinger <pholzing@redhat.com>
