minor: replica set test fixes

lib/mongo/node.rb

@@ -158,7 +158,7 @@ module Mongo
       if !config['hosts']
         message = "Will not connect to #{host_string} because it's not a member " +
           "of a replica set."
-        raise ReplicaSetConnectionError, message
+        raise ConnectionFailure, message
       end
     end
 
@@ -171,7 +171,7 @@ module Mongo
         elsif self.connection.replica_set_name != config['setName']
           message = "Attempting to connect to replica set '#{config['setName']}' on member #{host_string} " +
             "but expected '#{self.connection.replica_set_name}'"
-          raise ReplicaSetConnectionError, message
+          raise ConnectionFailure, message
         end
       end
     end

lib/mongo/repl_set_connection.rb

@@ -354,7 +354,7 @@ module Mongo
       if @primary_pool
         begin
           socket = @primary_pool.checkout
-          @sockets_to_pools[socket] = @primary
+          @sockets_to_pools[socket] = @primary_pool
           return socket
         rescue NoMethodError
         end

lib/mongo/util/pool_manager.rb

@@ -94,6 +94,7 @@ module Mongo
       @read_pool = manager.read_pool
       @arbiters = manager.arbiters
       @hosts = manager.hosts
+      @tags_to_pools = {}
     end
 
     def initialize_data