Use std::string on test function param

Use std::string on test function param

resource paths could be converted to std::string to support both of
platform v 2.4 & 3.0 by generate paths dynamically.
For this, test assertion functions need to receive std::string() param
for not to use '.c_str()' member function of std::string to all of
callers.

Change-Id: I3780673a757204fea7be1846726e8f15f14c449b
Signed-off-by: Kyungwook Tak <k.tak@samsung.com>