Fixed that connection string is returned for partitioned federated tables.

mysql-test/r/partition_federated.result:
  Fixed error message
mysql-test/suite/federated/federated_partition.result:
  Added test to show that connection string is returned in 'show create'.
sql/ha_partition.cc:
  Fixed a set of bugs introduced by the last federated patch:
  - We can't allocate m_ordered_rec_buffer in memroot as it has to survive call to clear_handler_file()
sql/partition_element.h:
  Ensure that connect_string is properly initialized.
  (This caused crashed in partition tests)
sql/sql_partition.cc:
  Print CONNECTION option for federated partitioned tables