[server][ArmCeilometer] Add a new arm for OpenStack's ceilometer.
[server][ArmBase] Remove an empty line.
[server][ArmBase] Add a mechanism to have a name that will be use mainly for messages.
[CodingConvention] Add a rule for a C++'s override method.
[server][ArmBase] Add a new method: synchronizeThreadExit().

The purpose of this patch is to clean up the destructor of
subclasses by aggregating commonly used code.
[server][ArmBase] Show a message so that subclasses can omit it.
[server][ArmZabbixAPI] Use synchronizeThreadExit() to make the destructor clean.
[server][ArmNagiosNDOUtils] Use synchronizeThreadExit() to make the destructor clean.
[server][ArmCeilometer] Use synchronizeThreadExit() to make the destructor clean.
[server][ArmBase] Remove an unnecessary AtomicValue, because the variable is used by only one thread.