[DBAgentTest] Suppress a waring due to a missing of a space.

In C++11 mode, the following warning is shown.

DBAgentTest.cc:949:36: warning: invalid suffix on literal; C++11 requires a space between literal and identifier [-Wliteral-suffix]
     dbAgent, checker, val, sprintf("hanako.%"PRIu64, id).c_str());