fix the following valgrind warning when running ndb_mgm -e show (leak only in client)

==20398== 14,596 (11,936 direct, 2,660 indirect) bytes in 4 blocks are definitely lost in loss record 24 of 25
==20398==    at 0x401C4A1: malloc (vg_replace_malloc.c:149)
==20398==    by 0x80797A3: ConfigValuesFactory::create(unsigned, unsigned) (ConfigValues.cpp:309)
==20398==    by 0x8079F03: ConfigValuesFactory::expand(unsigned, unsigned) (ConfigValues.cpp:325)
==20398==    by 0x8079967: ConfigValuesFactory::put(ConfigValues::Entry const&) (ConfigValues.cpp:414)
==20398==    by 0x807A7B6: ConfigValuesFactory::unpack(void const*, unsigned) (ConfigValues.cpp:701)
==20398==    by 0x806CB9D: ConfigValuesFactory::unpack(UtilBuffer const&) (ConfigValues.hpp:252)
==20398==    by 0x8069160: ndb_mgm_get_configuration (mgmapi.cpp:1941)
==20398==    by 0x8060661: CommandInterpreter::executeShow(char*) (CommandInterpreter.cpp:1242)
==20398==    by 0x8063966: CommandInterpreter::execute_impl(char const*) (CommandInterpreter.cpp:715)
==20398==    by 0x8064040: CommandInterpreter::execute(char const*, int, int*) (CommandInterpreter.cpp:625)
==20398==    by 0x8064189: Ndb_mgmclient::execute(char const*, int, int*) (CommandInterpreter.cpp:203)
==20398==    by 0x805E56C: read_and_execute(int) (main.cpp:124)
==20398==    by 0x805E754: main (main.cpp:162)
==20398==