Improve Zookeeper log handling

Ensures that messages are fully read before each append. Adds more
Zookeeper hits, but ensures logs won't be overwritten by multiple
daemons.

Also don't use a set on the client side, to avoid "removing duplicate"
entries erroneously.

client-cli/pvc/lib/node.py

@@ -142,9 +142,8 @@ def follow_node_log(config, node, lines=10):
         node_log = new_node_log
 
         # Get the difference between the two sets of lines
-        old_node_loglines_set = set(old_node_loglines)
         diff_node_loglines = [
-            x for x in new_node_loglines if x not in old_node_loglines_set
+            x for x in new_node_loglines if x not in old_node_loglines
         ]
 
         # If there's a difference, print it out