Factor tune_system() out of multinode-demo/ (#4138)

* Remove x bit from ulimit-n.sh

* Factor tune_system() out of multinode-demo/

multinode-demo/bootstrap-leader.sh

@@ -31,7 +31,11 @@ else
   program="$solana_fullnode"
 fi
 
-tune_system
+if [[ -z $CI ]]; then # Skip in CI
+  # shellcheck source=scripts/tune-system.sh
+  source "$SOLANA_ROOT"/scripts/tune-system.sh
+fi
+
 
 $solana_ledger_tool --ledger "$SOLANA_CONFIG_DIR"/bootstrap-leader-ledger verify