set COSA_DIR in Dockerfile

ci/Dockerfile

@@ -8,5 +8,14 @@ RUN go test -v -c -o layering_test ./tests/layering
 
 FROM registry.svc.ci.openshift.org/coreos/coreos-assembler:latest
 WORKDIR /src
+ENV COSA_DIR=/tmp/cosa
 COPY --from=builder /go/src/github.com/openshift/os/layering_test /usr/local/bin/layering_test
 COPY . .
+RUN mkdir -p "${COSA_DIR}"
+# We need to make sure that root can read / write to the COSA_DIR so that
+# when this container is actually run, we have permissions to read and
+# write to the COSA_DIR to allow the Kola tests to run.
+USER root
+RUN chgrp -Rf root "${COSA_DIR}" && \
+  chmod -Rf g+w "${COSA_DIR}"
+USER builder