Be more cautious about what images to pull

The set is different on different distro versions, so let's not let docker pull
fail, instead be more cautious about what versions we actually expect to exist.

Author: hhorak

test/run_test

@@ -686,14 +686,33 @@ run_upgrade_test ()
 {
   local ret=0
 
-    local upgrade_path="none 12 13 15 16 none" prev= act=
+    local upgrade_path= prev= act=
+    case $OS in
+        rhel8)
+            upgrade_path="none 12 13 15 16 none"
+            ;;
+        rhel9|c9s)
+            upgrade_path="none 13 15 16 none"
+            ;;
+        rhel10|c10s)
+            upgrade_path="none 13 15 16 none"
+            ;;
+        fedora)
+            upgrade_path="none 12 13 14 15 16 none"
+            ;;
+        *)
+            echo "unsupported OS variable" >&2
+            return 1
+            ;;
+    esac
+
     for act in $upgrade_path; do
         if test "$act" = $VERSION; then
             break
         fi
         prev=$act
     done
-    test "$prev" != none
+    test "$prev" != none || return 0
     # Check if the previous image is available in the registry
     docker pull "$(get_image_id "$prev:remote")" || return 0