Buildah and podman build can create images without a working dir.
FROM fedora
WORKDIR /test
If you build this image with caching twice, the second time the image
will not have a working dir.
Similarly if you execute
podman run --workdir /foobar fedora
It blows up since the workingdir is not created automatically.
Finally there was duplicated code for getting the workingdir
out of an image, that this PR removes.
Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>