[server][DBClientConfig] Make a build fail when 'new CacheServiceDBClient()' is called.
[server][DBClientConfig] Brush up a comment.
[server][DBClientConfig] Add a new method: getArmPluginInfo().
[server][testDBClientConfig] Add a new test: test_getArmPluginInfoWithTypeFail().
Merge pull request #196 from project-hatohol/issue-171

Issue 171