Mitigate newly added shellcheck issues

Issues not present when the original patch was created have now also
been fixed.

Signed-off-by: Joakim Roubert <joakim.roubert@axis.com>

cluster/gce/gci/configure-helper.sh

@@ -41,7 +41,7 @@ function convert-manifest-params {
   for flag in "${FLAGS[@]}"; do
     params+="\n\"$flag\","
   done
-  if [ -n "${params[*]}" ]; then
+  if [ -n "$params" ]; then
     echo "${params::-1}"  #  drop trailing comma
   fi
 }