[Tizen] Check signature value using xmlsec1 library

Based on API provided by xmlsec1 library, signature value and reference are checked.
from above code, second para of `xmlSecCryptoAppKeysMngrCertLoadMemory` is `const char*`, which is totally matched with `std::strcing::c_str()`. So I do not think the var `data` is required, maybe
```
    if (xmlSecCryptoAppKeysMngrCertLoadMemory(mngr, cert.c_str(), cert.size(),
                                              xmlSecKeyDataFormatCertPem,
                                              xmlSecKeyDataTypeTrusted) < 0) {
      ...
    }
```