add disk option to various bank tests


storage/ndb/test/include/NDBT_Tables.hpp:
  Make create_default_tablespace public
storage/ndb/test/ndbapi/bank/Bank.cpp:
  use const char*
storage/ndb/test/ndbapi/bank/Bank.hpp:
  add disk option
storage/ndb/test/ndbapi/bank/BankLoad.cpp:
  add disk option
storage/ndb/test/ndbapi/bank/bankCreator.cpp:
  Add disk option to bankCreator
storage/ndb/test/ndbapi/bank/testBank.cpp:
  use const char*
storage/ndb/test/ndbapi/testSRBank.cpp:
  Add disk option to testSRBank
storage/ndb/test/src/NDBT_Tables.cpp:
  Make create_default_tablespace public