ZOOKEEPER-4830. Replace references to zk_followers (apache#2160)

It was renamed to zk_learners in 290f1fc / ZOOKEEPER-3117, but many references weren't updated.

Author: PleasingFungus

zookeeper-contrib/zookeeper-contrib-huebrowser/zkui/src/zkui/templates/view.mako

@@ -96,7 +96,7 @@ ${shared.info_button(url('zkui.views.tree', id=cluster['id'], path='/'), 'View Z
     ${show_stats(leader)}
 
     <tr><td>Followers</td>
-      <td>${leader.get('zk_followers', '')}</td>
+      <td>${leader.get('zk_learners', '')}</td>
     </tr>
 
     <tr><td>Synced Followers</td>

zookeeper-contrib/zookeeper-contrib-monitoring/ganglia/zookeeper.pyconf

@@ -43,7 +43,7 @@ collection_group {
   metric { name = "zk_approximate_data_size" }
   metric { name = "zk_open_file_descriptor_count" }
   metric { name = "zk_max_file_descriptor_count" }
-  metric { name = "zk_followers" }
+  metric { name = "zk_learners" }
   metric { name = "zk_synced_followers" }
   metric { name = "zk_pending_syncs" }
   metric { name = "zk_last_proposal_size" }

zookeeper-contrib/zookeeper-contrib-monitoring/ganglia/zookeeper_ganglia.py

@@ -212,7 +212,7 @@ def metric_init(params=None):
         'zk_approximate_data_size': {'units': 'bytes'},
         'zk_open_file_descriptor_count': {'units': 'descriptors'},
         'zk_max_file_descriptor_count': {'units': 'descriptors'},
-        'zk_followers': {'units': 'nodes'},
+        'zk_learners': {'units': 'nodes'},
         'zk_synced_followers': {'units': 'nodes'},
         'zk_pending_syncs': {'units': 'syncs'},
         'zk_last_proposal_size': {'units': 'bytes'},

zookeeper-docs/src/main/resources/markdown/zookeeperAdmin.md

@@ -2490,7 +2490,7 @@ Moving forward, Four Letter Words will be deprecated, please use
                   zk_watch_count  0
                   zk_ephemerals_count 0
                   zk_approximate_data_size    27
-                  zk_followers    4                   - only exposed by the Leader
+                  zk_learners    4                    - only exposed by the Leader
                   zk_synced_followers 4               - only exposed by the Leader
                   zk_pending_syncs    0               - only exposed by the Leader
                   zk_open_file_descriptor_count 23    - only available on Unix platforms