Add cluster backup + restore functionality

Adds cluster backup (JSON dump) and restore functions for use in
disaster recovery.

Further, adds additional confirmation to the initialization (as well as
restore) endpoints to avoid accidental triggering, and also groups the
init, backup, and restore commands in the CLI into a new "task"
subsection.

api-daemon/pvcapid/helper.py

@@ -21,6 +21,7 @@
 ###############################################################################
 
 import flask
+import json
 import lxml.etree as etree
 
 from distutils.util import strtobool as dustrtobool
@@ -49,7 +50,7 @@ def strtobool(stringv):
 
 
 #
-# Initialization function
+# Cluster base functions
 #
 def initialize_cluster():
     # Open a Zookeeper connection
@@ -86,6 +87,66 @@ def initialize_cluster():
     return True
 
 
+def backup_cluster():
+    # Open a zookeeper connection
+    zk_conn = pvc_common.startZKConnection(config['coordinators'])
+
+    # Dictionary of values to come
+    cluster_data = dict()
+
+    def get_data(path):
+        data_raw = zk_conn.get(path)
+        if data_raw:
+            data = data_raw[0].decode('utf8')
+        children = zk_conn.get_children(path)
+
+        cluster_data[path] = data
+
+        if children:
+            if path == '/':
+                child_prefix = '/'
+            else:
+                child_prefix = path + '/'
+
+            for child in children:
+                if child_prefix + child == '/zookeeper':
+                    # We must skip the built-in /zookeeper tree
+                    continue
+                get_data(child_prefix + child)
+
+    get_data('/')
+
+    return cluster_data, 200
+
+
+def restore_cluster(cluster_data_raw):
+    # Open a zookeeper connection
+    zk_conn = pvc_common.startZKConnection(config['coordinators'])
+
+    # Open a single transaction (restore is atomic)
+    zk_transaction = zk_conn.transaction()
+
+    try:
+        cluster_data = json.loads(cluster_data_raw)
+    except Exception as e:
+        return {"message": "Failed to parse JSON data: {}.".format(e)}, 400
+
+    for key in cluster_data:
+        data = cluster_data[key]
+
+        if zk_conn.exists(key):
+            zk_transaction.set_data(key, str(data).encode('utf8'))
+        else:
+            zk_transaction.create(key, str(data).encode('utf8'))
+
+    try:
+        zk_transaction.commit()
+        return {'message': 'Restore completed successfully.'}, 200
+    except Exception as e:
+        raise
+        return {'message': 'Restore failed: {}.'.format(e)}, 500
+
+
 #
 # Cluster functions
 #