[HatoholException] A new helper class: ExceptionCatchable.
[testHatoholException] Add a new test: test_catchStdException().
[testHatoholException] Add a new test: test_catchUnknownException().
[testHatoholException] Clean up.
[DBClientAction] Use ExceptionCatachable to make code simple.
[ExceptionCatchable] Fix a typo in a comment

ExceptionCatcher ->
ExceptionCatchable
Merge pull request #322 from project-hatohol/exception-catcher2

Exception catcher2