Update only selected attributes for winsync agreement

Trying to insert nsDS5ReplicatedAttributeListTotal and
nsds5ReplicaStripAttrs to winsync agreements caused upgrade errors.
With this patch, these attributes are skipped for winsync agreements.

Made find_ipa_replication_agreements() in replication.py more
corresponding to find_replication_agreements. It returns list of
entries instead of unicode strings now.

https://fedorahosted.org/freeipa/ticket/3522

ipaserver/install/replication.py

@@ -307,20 +307,15 @@ class ReplicationManager(object):
         Return the list of hosts we have replication agreements.
         """
 
-        res = []
-
         filt = self.get_agreement_filter(IPA_REPLICA)
         try:
             ents = self.conn.get_entries(
                 DN(('cn', 'mapping tree'), ('cn', 'config')),
                 ldap.SCOPE_SUBTREE, filt)
         except errors.NotFound:
-            return res
+            ents = []
 
-        for ent in ents:
-            res.append(ent.single_value('nsds5replicahost', None))
-
-        return res
+        return ents
 
     def get_replication_agreement(self, hostname):
         """