[KeyManager] generateKeyPair implementation

[KeyManager] generateKeyPair implementation

[Verification]
var myPrivKey = new tizen.Key("priv3", "priv_password", false);
var myPubKey = new tizen.Key("pub3", null, true);

tizen.keymanager.generateKeyPair(myPrivKey, myPubKey, "RSA", "2048", function() {
    console.log('ok');
  }, function(e) {
    console.log(e.code);
    console.log(e.message);
});

Change-Id: I6d59104f2d8d0f0022ed64b83a6036e10dd9f306
Signed-off-by: Przemyslaw Ciezkowski <p.ciezkowski@samsung.com>