shill: wifi: Enable use of hardware-backed certificate credentials

Enable use of hardware-backed certificates and keys by enabling
the pkcs11 module for wpa_supplicant.  Bonus change: Enable use
of system CAs by default, although it is expected that Chrome
sets this explicitly in all interesting cases.

BUG=chromium-os:29462
TEST=New unit tests.  Manual: Connect to EAP-TLS network using hardware
backed certs.

Change-Id: I9909f25be1007a56f2b9830a03f26cb6b7931968
Reviewed-on: https://gerrit.chromium.org/gerrit/20332
Commit-Ready: Paul Stewart <pstew@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
diff --git a/service.h b/service.h
index 8acd313..970525c 100644
--- a/service.h
+++ b/service.h
@@ -111,7 +111,7 @@
     kStateOnline
   };
   struct EapCredentials {
-    EapCredentials() : use_system_cas(false) {}
+    EapCredentials() : use_system_cas(true) {}
     std::string identity;
     std::string eap;
     std::string inner_eap;