BUG#22305  	SysLogHandler not thread safe
BUG#22313  	can get duplicate log messages in cluster log

Fix all these problems with one patch. Make Logger, hence EventLogger (with a 
bit more) thread safe.


storage/ndb/include/debugger/EventLogger.hpp:
  remove m_text to make thread safe
storage/ndb/include/logger/Logger.hpp:
  Use mutex to protect member variables for multithreaded use.
storage/ndb/src/common/debugger/EventLogger.cpp:
  use a string on the stack instead of member variable to make class thread safe
storage/ndb/src/common/logger/Logger.cpp:
  use mutexes to Guard member variables. makes class therad safe