[server][DBClientHatohol] Add comments.
[server][ArmZabbixAPI] Eliminate disinterested host groups.

For example, 'Templates' and 'Discovered hosts' are not needed.
[server][DBClientHatohol] Use a join with the hostgroup table for getting a trigger list only when it's really needed.
[server][DBClientHatohol] Restore the indent that was mistakenly changed in the previous commit.
[server][DBClientHatohol] Use a join with the hostgroup table for getting an item list only when it's really needed.
[server][DBClientHatohol] Use a join with the hostgroup table for getting a host list only when it's really needed.
[server][DBClientHatohol] Fix a bug that passes a wrong column of host id by mistake.