Security manager is not a dynamically loadable driver, it's a common
infrastructure similar to util, conf, cpu, etc. used by individual
drivers. Such code is allowed to be linked into libvirt.so.

This reverts commit ec5b7bd2 and most of
aae5cfb6.

This patch is supposed to fix virdrivermoduletest failures for qemu and
lxc drivers as well as libvirtd's ability to load qemu and lxc drivers.