[Flaky test] Disable flaky zookeeper tests (#43381)

Disable the flaky test `metricbeat/module/zookeeper/test_zookeeper`, reported in #43385.

Also add a message to the failing assertions indicating the actual data the tests failed on, so when a failure does happen we can see what caused it.

(cherry picked from commit 9e29bcb)

Author: faec

metricbeat/module/zookeeper/test_zookeeper.py

@@ -14,6 +14,7 @@
                "approximate_data_size", "num_alive_connections"]
 
 
+@unittest.skip("flaky test suite: https://github.com/elastic/beats/issues/43385")
 @metricbeat.parameterized_with_supported_versions
 class ZooKeeperMntrTest(metricbeat.BaseTest):
 
@@ -37,7 +38,7 @@ def test_output(self):
         self.assert_no_logged_warnings()
 
         output = self.read_output_json()
-        self.assertEqual(len(output), 1)
+        self.assertEqual(len(output), 1, f"expected one output result, got: {output}")
         evt = output[0]
 
         self.assertCountEqual(self.de_dot(ZK_FIELDS), evt.keys())
@@ -71,7 +72,7 @@ def test_output(self):
         self.assert_no_logged_warnings()
 
         output = self.read_output_json()
-        self.assertEqual(len(output), 1)
+        self.assertEqual(len(output), 1, f"expected one output result, got: {output}")
         evt = output[0]
 
         self.assertCountEqual(self.de_dot(ZK_FIELDS), evt.keys())
@@ -99,7 +100,7 @@ def test_connection(self):
         self.assert_no_logged_warnings()
 
         output = self.read_output_json()
-        self.assertEqual(len(output), 1)
+        self.assertEqual(len(output), 1, f"expected one output result, got: {output}")
         evt = output[0]
 
         self.assertCountEqual(self.de_dot(ZK_FIELDS + ["client"]), evt.keys())