lb: fix haproxy cannot start if algorithm is not lowercase (#9698)

Author: weizhouapache

core/src/main/java/com/cloud/network/HAProxyConfigurator.java

@@ -484,7 +484,7 @@ private List<String> getRulesForPool(final LoadBalancerTO lbTO, final boolean ke
         sb.append("\tbind ").append(publicIP).append(":").append(publicPort);
         result.add(sb.toString());
         sb = new StringBuilder();
-        sb.append("\t").append("balance ").append(algorithm);
+        sb.append("\t").append("balance ").append(algorithm.toLowerCase());
         result.add(sb.toString());
 
         int i = 0;