run_unix: don't return an error from getNetworkInterface
run_unix: don't return an error from getNetworkInterface

While networking is not supported on non-Linux systems, many
operations can still succeed if we allow buildah to proceed without a
NetworkInterface object.

To do so, don't return an error from getNetworkInterface.

Signed-off-by: Sergio Lopez <2a49a3230a2bdfb748295d04d38c6f188489c774@redhat.com>

TomSweeneyRedHat/buildah,nalind/buildah-1,nalind/buildah-1,nalind/buildah-1,TomSweeneyRedHat/buildah,TomSweeneyRedHat/buildah