security: Don't add seclabel of type none if there's already a seclabel
security: Don't add seclabel of type none if there's already a seclabel

https://bugzilla.redhat.com/show_bug.cgi?id=923946

The <seclabel type='none'/> should be added iff there is no other
seclabel defined within a domain. This bug can be easily reproduced:
1) configure selinux seclabel for a domain
2) disable system's selinux and restart libvirtd
3) observe <seclabel type='none'/> being appended to a domain on its
   startup
(cherry picked from commit e4a28a328188e715de8d587b390cb44e2d6c3fb4)

mithleshvrts/libvirt-0.10.2,mithleshvrts/libvirt-0.10.2,mithleshvrts/libvirt-0.10.2,mithleshvrts/libvirt-0.10.2,mithleshvrts/libvirt-0.10.2