[server][HatoholThreadBase] Clean up.
[server][HatoholThreadBase] Add a mechanism to execute mainThread() when an exception is caught.
[server][testHatoholThreadBase] Add a new test_cancelReexecSleep().
[server][HatoholThreadBase] Add a mechanism for the exit.
[server][testHatoholThreadBase] Clean up.
[server][testArmZabbixAPI] Replace the exception callback mechanism with that with virtual method.
[server][HatoholThreadBase] Remove the old exception notification mechanism that is no longer used.
[server][HatoholThreadBase] Add a new method: requestExit().
[server][HatoholArmPluginGate] Use the base class (HatoholThreadBase)'s reexecution mechanism instead of its own one.
[server][HatoholArmPluginGate] Merge issue-171.
Merge pull request #213 from project-hatohol/issue-171-2

Issue 171-2: Catch exception and reexecute smartly