[DBClientConfig] Use DBAgent::transaction() to make code C++ like.
[DBClientConfig] Use getDBAgent().transaction() for one line operations.
[test] Fix the build error due to the recent change of DBClientConfig::getDBAgent().
[DBClientConfig] Use getDBAgent().transaction() in addTargetServer().
[DBClientConfig] Use getDBAgent().transaction() in updateTargetServer().
[DBClientConfig] Use getDBAgent().transaction() in deleteTargetServer().
[DBClientConfig] Use getDBAgent().transaction() in saveArmPluginInfo().
[DBClientConfig] Use getDBAgent().transaction() in updateIncidentTracker().
[DBClientConfig] Fix a wrong code by mistake.
[DBClientConfig] Shorten long conditions of if statements
[DBClientConfig] Use functions to shorten conditions of if statements
Merge pull request #394 from project-hatohol/trx-config

Use DBAgent()::transaction instead of DBCLINET_TRANSACTION_BEGIN() macro.
The previous statement with the marco has broken the C++ syntax grammar and
seems to a little storange.