Add UnifiedDataStore class to solve confusing VirtualDataStore usage
Fix typo
Build UnifiedDataStore.{cc,h}
Add VirtualDataStore{Zabbix,Nagios} to UnifiedDataStore
Remove needless inheritance
Add UnifiedDataStore::stop() and change start() to virtual.
Replace VirtualDataStore{Zabbix,Nagios} in ExecContext and FaceRest with UnifiedDataStore
Also ItemInfoList should be fetched via UnifiedDataStore.

Sorry, I forgot to replace it at project-hatohol/hatohol@4e907f0.
Add a test case for UnifiedDataStore
Use testTriggerInfo as expected value of testUnifiedDataStore::test_getTriggerList.

Since I've noticed that currently this test should be same with
testDBClientHatohol::test_testGetTriggerInfoList, I use same
expected data at this time. On the other hand these implementations
may become different in the future because VirtualDataStore* may
have other data sources (such as on-memory data). So I leave this
test.
Remove needless include
fixed the wrong format string for a size_t variable.

%d ->
%zd
fixed the wrong format strings for int (enum'ed) variables.

%zd ->
%d
Set suitable DB path for testUnifiedDataStore.

We should set the path of DB_DOMAIN_ID_HATOHOL for testing
UnifiedDataStore, not DEAFAULT_DB_DOMAIN_ID.
In addition we use fixtures/testDatabase-hatohol.db for testing it
since currently UnifiedDataStore is read-only.
fixed the wrong format strings for int (enum'ed) variables.

%zd ->
%d
fixed the wrong format string for a size_t variable.

%d ->
%zd
fixed the wrong format string for a size_t variable.

%d ->
%zd
fixed the wrong format string for a size_t variable.

%d ->
%zd
fixed the wrong format strings for an int (enum'ed) variable.

%zd ->
%d
removed an needless space.