If two shards differ we need to sync

There's no security if two shards return different answers but it gives
us enough of a signal to know that we need to trigger a full on
synchronization.

BugzId: 18955

src/mem3_sync_security.erl

@@ -35,6 +35,8 @@ maybe_sync_int(#shard{name=Name}=Src, Dst) ->
                 1 -> ok;
                 2 -> go(DbName)
             end;
+        {error, no_majority} ->
+            go(DbName);
         Else ->
             Args = [DbName, Else],
             couch_log:error("Error checking security objects for ~s :: ~p", Args)