pkcs11: use generic evp key instead of rsa

Enables DSA, ECDSA key usages with newer pkcs11-helper.

Signed-off-by: Alon Bar-Lev <alon.barlev@gmail.com>
Tested-By: Sanaullah <sanaullah82@gmail.com>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <1384209366-26170-1-git-send-email-alon.barlev@gmail.com>
URL: http://article.gmane.org/gmane.network.openvpn.devel/7960
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 6575ad483702dd53c0f683093b5f26a87518c6a8)