Add replicafrom tag.

patroni/__init__.py

@@ -29,6 +29,10 @@ class Patroni:
     def nofailover(self):
         return self.tags.get('nofailover', False)
 
+    @property
+    def replicatefrom(self):
+        return self.tags.get('replicatefrom')
+
     @staticmethod
     def get_dcs(name, config):
         if 'etcd' in config:

patroni/dcs.py

@@ -67,6 +67,10 @@ class Member(namedtuple('Member', 'index,name,session,data')):
     def nofailover(self):
         return self.data.get('tags', {}).get('nofailover', False)
 
+    @property
+    def replicatefrom(self):
+        return self.data.get('tags', {}).get('replicatefrom')
+
 
 class Leader(namedtuple('Leader', 'index,session,member')):