CI: give the rootless test user some supplemental groups

Exercise preservation of supplemental groups in the tests that use
`buildah build` and `buildah from` with `--group-add keep-groups`.

Signed-off-by: Nalin Dahyabhai <[email protected]>

Author: nalind

contrib/cirrus/lib.sh

@@ -298,9 +298,12 @@ setup_rootless() {
     # Guarantee independence from specific values
     rootless_uid=$[RANDOM+1000]
     rootless_gid=$[RANDOM+1000]
-    msg "creating $rootless_uid:$rootless_gid $ROOTLESS_USER user"
+    rootless_supplemental_gid=$[RANDOM+1000]
+    msg "creating $rootless_uid:$rootless_gid,$rootless_supplemental_gid $ROOTLESS_USER user"
     groupadd -g $rootless_gid $ROOTLESS_USER
-    useradd -g $rootless_gid -u $rootless_uid --no-user-group --create-home $ROOTLESS_USER
+    groupadd -g $rootless_supplemental_gid ${ROOTLESS_USER}sg
+    useradd -g $rootless_gid -G ${ROOTLESS_USER}sg -u $rootless_uid --no-user-group --create-home $ROOTLESS_USER
+    id $ROOTLESS_USER
 
     # We also set up rootless user for image-scp tests (running as root)
     if [[ $PRIV_NAME = "rootless" ]]; then