Fix bug in event handling wrt early node shutdown


ndb/src/mgmsrv/MgmtSrvr.cpp:
  Fix bug in event handling wrt early node shutdown
ndb/src/ndbapi/ClusterMgr.cpp:
  Fix reportNodeFailed if only connected wo/ having received any API_REGCONF
ndb/src/ndbapi/ClusterMgr.hpp:
  Fix reportNodeFailed if only connected wo/ having received any API_REGCONF
ndb/src/ndbapi/SignalSender.cpp:
  Fix memleak