fix paired connection find master

lib/mongo/db.rb

@@ -154,11 +154,11 @@ module Mongo
           is_master = master?
           @semaphore.lock if semaphore_is_locked
 
-          break if @slave_ok || is_master
+          @slave_ok || is_master
         rescue SocketError, SystemCallError, IOError => ex
           close if @socket
+          false
         end
-        @socket
       }
       raise "error: failed to connect to any given host:port" unless @socket
     end