run-unit-test-docker: support podman

podman requires this env variable be set in order to have the correct
permissions to mount your home filesystem.

Tested:
- Verified after the latest sdbusplus updates that this script can now
  run on a POWER9 based server using RH8 + podman

Change-Id: I32a9e68f8cfc5df1d4489a2e089ab3ba92558cc9
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/run-unit-test-docker.sh b/run-unit-test-docker.sh
index 5ff16c5..95f0e33 100755
--- a/run-unit-test-docker.sh
+++ b/run-unit-test-docker.sh
@@ -99,6 +99,10 @@
         --env ftp_proxy=${http_proxy}"
 fi
 
+# If we are building on a podman based machine, need to have this set in
+# the env to allow the home mount to work (no impact on non-podman systems)
+export PODMAN_USERNS="keep-id"
+
 # shellcheck disable=SC2086 # ${PROXY_ENV} and ${EXTRA_DOCKER_RUN_ARGS} are
 # meant to be split
 docker run --cap-add=sys_admin --rm=true \