changed the type of DB domain definitions.

int ->
DBDomainId

They should be handled as the specific type.
aligned values of DB domain ID definition.
changed the actual DB of DBClientConfig to MySQL.

This is a part of the work to support HA configuration of Hatohol.
In that case, the configuration DB is accessed from multiple
Hatohol servers. So we use MySQL that is client-server type DB.
removed the test config DB for SQLite3 because we will use MySQL as the configuration DB.
moved makeTEstDBIfNeeded() to Helpers as makeTestMySQLDBIfNeeded() to use it from other tests.
added a behavior to pass NULL if hostname, username, or password is empty.

MySQL recognizes "" as an empty string password, not NULL
(no password is used).
Actually empty password is not used. So we add this behavior.
fixed the setups to execute testDBClientConfig.

This fix mainly changes the way to connect with the DB and
drop the database for the test.
added code to work the setup of DBAgentMySQL.

DBAgentMySQL has been used only for NagiosNDOUtils. So the setup such
create tables is not fully implemented, because only read-out from the
DB was needed.
fixed testDBClientConfig::test_createDB() for DBClientConfig on DBAgentMySQL.
rewrote testDBClientConfig::test_createDB() without the dependency on the actual DBAgent object.

We'll apply the similar way to other existing tests that depends
on the acteual DBAgent object (i.e. DBAgentSQLite3 or DBAgentMySQL)
implemented DBAgentMySQL::isTableExisting().
add testDBAgentSQLite3::test_isTableExisting().

This function uses dbAgentTestIsTableExisting() added the previous
commit.
wrapped a long line to be within 80 digits.
implemented DBAgentMySQL::isRecordExisting().
added a utility method: DBAgentMySQL::execSql().
replaced code calling mysql_query() with execSql() to make source code simple.
implemeted begin90, commit(), and rollback() of DBAgentMySQL.
removed the redundant word (test) in test function names.
fixed test_addTargetServer() to work with DBAgent-indepent helper functions.
fixed testDBClientConfig().