libvirt-auth: Provide a friendlier wrapper around virConnectAuthPtrDefault (RHBZ#1044014).
tests: Add a regression test of libvirt authentication events.

This requires a change to libvirt (in libvirt >= 1.2.1), see:

https://www.redhat.com/archives/libvir-list/2014-January/msg00378.html
tests: Add a regression test for libvirt authentication (RHBZ#1044014).

This tests the virConnectAuthPtrDefault wrapper path.