Restart libvirtd after config file changed

When a compute node changes to a new virtualization host,
/etc/libvirtd/qemu.conf is changed, and libvirtd needs to get
restarted to make the change effective. To avoid timing problems,
all packages have to be installed on the system, before the libvirtd
restart check happens
Merge pull request #271 from nkrinner/bnc829514-roxy

Restart libvirtd after config file changed