Refactor secret check

Moving the check to start allows invalid configurations to be fixed via
JMX and changes to be made followed by stop()/start() for those changes
to take effect.

java/org/apache/coyote/ajp/AbstractAjpProtocol.java

@@ -267,13 +267,13 @@ protected Processor createUpgradeProcessor(SocketWrapperBase<?> socket,
 
 
     @Override
-    public void init() throws Exception {
+    public void start() throws Exception {
         if (getSecretRequired()) {
             String secret = getSecret();
             if (secret == null || secret.length() == 0) {
                 throw new IllegalArgumentException(sm.getString("ajpprotocol.nosecret"));
             }
         }
-        super.init();
+        super.start();
     }
 }