[Mac OS X] Secure Transport integration forces keychain write access for custom key pair

In the Qt 5.6 the default SSL backend was changed to Secure Transport on the Mac OS platform.

This has the consequence that when custom certificate and private key is added to QSslConfiguration they are also written to the keychain (due to the SecPkcs12Import call).

This does not work when application runs as a launchd daemon or for example under 'daemon' account (sudo -u daemon ./testapp).

The QAbstractSocket::SslInvalidUserDataError error is triggered with "SecPKCS12Import returned no items" description.