[JENKINS-27035] Gathering command read/write events (#3071)

* Slave.JnlpJar.getURL did not work in some modes when core had a snapshot dependency on Remoting.

* Starting to implement Channel.Listener.read/write.

* Now obtaining response timing statistics.

* For now, avoiding timestamped snapshots, as it caused problems for #3120 which I have asked for help from @stephenc diagnosing.

* Simplified logging a bit.

* onResponse

* hudson.FilePath$Mkdirs is a lot more readable than hudson.FilePath$13.

* Specific snapshot.

* onJar

* LoggingChannelListener

* remoting.version=3.17

* Making a few test assertions more lenient to adapt to https://github.com/jenkinsci/remoting/pull/247.

core/src/main/java/hudson/FilePath.java

@@ -1167,19 +1167,22 @@ public final class FilePath implements Serializable {
      * Creates this directory.
      */
     public void mkdirs() throws IOException, InterruptedException {
-        if(!act(new SecureFileCallable<Boolean>() {
-            private static final long serialVersionUID = 1L;
-            public Boolean invoke(File f, VirtualChannel channel) throws IOException, InterruptedException {
-                if(mkdirs(f) || f.exists())
-                    return true;    // OK
+        if (!act(new Mkdirs())) {
+            throw new IOException("Failed to mkdirs: " + remote);
+        }
+    }
+    private class Mkdirs extends SecureFileCallable<Boolean> {
+        private static final long serialVersionUID = 1L;
+        @Override
+        public Boolean invoke(File f, VirtualChannel channel) throws IOException, InterruptedException {
+            if(mkdirs(f) || f.exists())
+                return true;    // OK
 
-                // following Ant <mkdir> task to avoid possible race condition.
-                Thread.sleep(10);
+            // following Ant <mkdir> task to avoid possible race condition.
+            Thread.sleep(10);
 
-                return mkdirs(f) || f.exists();
-            }
-        }))
-            throw new IOException("Failed to mkdirs: "+remote);
+            return mkdirs(f) || f.exists();
+        }
     }
 
     /**
@@ -2828,6 +2831,11 @@ public final class FilePath implements Serializable {
             return classLoader;
         }
 
+        @Override
+        public String toString() {
+            return callable.toString();
+        }
+
         private static final long serialVersionUID = 1L;
     }