ZOOKEEPER-4200: Widen latency window in WatcherCleanerTest

`WatcherCleanerTest` performs latency checks which fail when outside of a 20+Xms window.  Before this patch, X was 5ms—whereas 30+ms is frequently seen on an i5 Mac Mini running macOS Catalina.

This "dumb" patch just widens the window to 20ms, which makes it "work on my machine," but could obviously still fail in a loaded environment or VM.

Author: Damien Diederen <dd@crosstwine.com>

Reviewers: Enrico Olivelli <eolivelli@apache.org>, Mate Szalay-Beko <symat@apache.org>

Closes #1592 from ztzg/ZOOKEEPER-4200-widen-latency-window

zookeeper-server/src/test/java/org/apache/zookeeper/server/watch/WatcherCleanerTest.java

@@ -162,13 +162,13 @@ public class WatcherCleanerTest extends ZKTestCase {
 
         assertEquals(3L, values.get("cnt_dead_watchers_cleaner_latency"));
 
-        //Each latency should be a little over 20 ms, allow 5 ms deviation
-        assertEquals(20D, (Double) values.get("avg_dead_watchers_cleaner_latency"), 5);
-        assertEquals(20D, ((Long) values.get("min_dead_watchers_cleaner_latency")).doubleValue(), 5);
-        assertEquals(20D, ((Long) values.get("max_dead_watchers_cleaner_latency")).doubleValue(), 5);
-        assertEquals(20D, ((Long) values.get("p50_dead_watchers_cleaner_latency")).doubleValue(), 5);
-        assertEquals(20D, ((Long) values.get("p95_dead_watchers_cleaner_latency")).doubleValue(), 5);
-        assertEquals(20D, ((Long) values.get("p99_dead_watchers_cleaner_latency")).doubleValue(), 5);
+        //Each latency should be a little over 20 ms, allow 20 ms deviation
+        assertEquals(20D, (Double) values.get("avg_dead_watchers_cleaner_latency"), 20);
+        assertEquals(20D, ((Long) values.get("min_dead_watchers_cleaner_latency")).doubleValue(), 20);
+        assertEquals(20D, ((Long) values.get("max_dead_watchers_cleaner_latency")).doubleValue(), 20);
+        assertEquals(20D, ((Long) values.get("p50_dead_watchers_cleaner_latency")).doubleValue(), 20);
+        assertEquals(20D, ((Long) values.get("p95_dead_watchers_cleaner_latency")).doubleValue(), 20);
+        assertEquals(20D, ((Long) values.get("p99_dead_watchers_cleaner_latency")).doubleValue(), 20);
     }
 
 }