daemon: Export SDL audio environment variables

daemon: Export SDL audio environment variables

/etc/sysconfig/libvirtd has a few environment variables for configuring
libvirt SDL audio. The libvirtd process doesn't see these, however, because
they are never exported. Let's export the variables after sourcing the
sysconfig script.

There is another problem here that the commented out values in the
sysconfig script are not neccessarily the actual defaults, we are qemus
mercy here. Not sure how to solve that.