pkcs11: Load p11-kit-proxy.so module by default

If the user specifies --pkcs11-id or --pkcs-id-management but neglects
to explicitly provide a --pkcs11-provider argument, and if the system
has p11-kit installed, then load the p11-kit proxy module so that the
system-configured tokens are available.

Trac: 490
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <1418303015.31745.78.camel@infradead.org>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9342
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 6f1d3cf062d5c33cbad4d521d157d43d53ffc7d1)
Make 'provider' option to --show-pkcs11-ids optional where p11-kit is present

Trac: 490
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <1418905506.21260.6.camel@infradead.org>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9355
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit a91a06cb291414c9e657377e44f7a57343ae7f5a)