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

SUSE-internal reference: bnc#829514

Syntax error with libvirt restart fixed
Merge pull request #251 from nkrinner/bnc829514

Restart libvirtd after config file changed