Fixed the problem that performs a DB setup every DBClientConnectable's instance creation.
Remove needless blank lines.
Clean up DBClientHatohol with DBClientConnectable.
Update a comment.
Make DBClientZabbix instances without a lock after the second time, because they don't have to do the setup.
Initialize DBClientConfig before hatoholInit(), because DBClientConfig::parseCommandLineArgument needs it.
Fix hatohol-config-db-creator to create a table: action and grant it.
Hide the call of init(), which is an irrelative thing for the class users.
Add an option to create MySQL's tables on the memory.

This is mainly for quick test.