Plumb --wait-for-supermajority through scripts (#10611) (#10613)

(cherry picked from commit 348bf78cd1)

Co-authored-by: Trent Nelson <trent@solana.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

multinode-demo/validator.sh

@@ -152,6 +152,9 @@ while [[ -n $1 ]]; do
     elif [[ $1 = --max-genesis-archive-unpacked-size ]]; then
       args+=("$1" "$2")
       shift 2
+    elif [[ $1 == --wait-for-supermajority ]]; then
+      args+=("$1" "$2")
+      shift 2
     elif [[ $1 = -h ]]; then
       usage "$@"
     else