Test for presence of /dev/kvm before setting permissions

In a native QEMU environment there is no /dev/kvm.

Change-Id: I4d0eb32fd6fad3a4c9c15c7c2b12430b2e4db154

docker/nova-compute/nova-libvirt/start.sh

 #!/bin/sh
 
 # If libvirt is not installed on the host permissions need to be set
-chmod 660 /dev/kvm
-chown root:kvm /dev/kvm
+# If running in qemu, we don't need to set anything as /dev/kvm won't exist
+if [[ -c /dev/kvm ]]; then
+    chmod 660 /dev/kvm
+    chown root:kvm /dev/kvm
+fi
 
 echo "Starting libvirtd."
 exec /usr/sbin/libvirtd