[Monitoring] Add some new members to ItemInfo

* valueType
* unit
[Monitoring] Fix typo

ITEM_INFO_VALUE_STRING ->
ITEM_INFO_VALUE_TYPE_STRING
[HatoholDBUtils] Store unit & value type in Zabbix's response to ItemInfo
[ArmNagiosNDOUtils] Fill valueType in ItemInfo with ITEM_INFO_VALUE_TYPE_STRING
[HapProcessCeilometer] Fill unit and valueType of ItemInfo
[DBTablesTest] Fill remaining members of ItemInfo
[HatoholDBUtils] Fix a wrong ITEM_ID in transformItemItemGroupToItemInfo()

ITEM_ID_ZBX_ITEMS_UNITS ->
ITEM_ID_ZBX_ITEMS_VALUE_TYPE
[server][test] Fix some broken test related with new members of ItemInfo

Tests still fail because the new members aren't stored to DB yet.
[DBTablesMonitoring] Enable to get/store new members of ItemInfo to DB

A test still fails because the reverse conversion of valueType
isn't cared yet.
[HapProcessCeilometer][HatoholDBUtils] Fix wrong value for valueType

Must use zabbix's valueType in current implementation.

TODO: We should remove zabbix dependency from HAPI's spec.
[RestResourceHost] Add new properties to items JSON

* unit
* valueType
[hatohol-def-src-file-generator] Add ItemInfoValueType
[server][doc] Add description about new properties of items
[DBTablesTest] Add a test data for "unit" of ItemInfo
Merge pull request #718 from project-hatohol/extend-item-info

Extend item info