Testcases for NF


ndb/src/kernel/blocks/ERROR_codes.txt:
  Error insert for testing NF handling of committed read
ndb/src/kernel/blocks/dblqh/DblqhMain.cpp:
  Error insert for testing NF handling of committed read
ndb/src/kernel/blocks/dbtc/DbtcMain.cpp:
  Error insert for testing NF handling of committed read
ndb/test/include/NDBT_Test.hpp:
  Move sync methods into NDBT_Context
ndb/test/ndbapi/testIndex.cpp:
  Move sync methods into NDBT_Context
ndb/test/ndbapi/testNodeRestart.cpp:
  Add test case that verifies committed read during NF
ndb/test/src/NDBT_Test.cpp:
  Move sync methods into NDBT_Context