Fix 'virsh domcapabilities' error

Calling `virsh domcapabilities ...` produces an error with some older
versions of libvirt:

    error: failed to get emulator capabilities
    error: invalid argument: unable to find any emulator to serve 'x86_64' architecture

The issue seems fixed if `virsh capabilites` is run first.

diff --git a/cmd/virt-launcher/node-labeller/node-labeller.sh b/cmd/virt-launcher/node-labeller/node-labeller.sh
index 8ea181963..55a920bdd 100755
--- a/cmd/virt-launcher/node-labeller/node-labeller.sh
+++ b/cmd/virt-launcher/node-labeller/node-labeller.sh
@@ -13,8 +13,10 @@ chmod o+rw /dev/kvm
 
 libvirtd -d
 
+virsh capabilities > /dev/null
+
 virsh domcapabilities --machine q35 --arch x86_64 --virttype kvm > /var/lib/kubevirt-node-labeller/virsh_domcapabilities.xml
 
 cp -r /usr/share/libvirt/cpu_map /var/lib/kubevirt-node-labeller
 
-virsh domcapabilities --machine q35 --arch x86_64 --virttype kvm | virsh hypervisor-cpu-baseline --features /dev/stdin --machine q35 --arch x86_64 --virttype kvm > /var/lib/kubevirt-node-labeller/supported_features.xml
\ No newline at end of file
+virsh domcapabilities --machine q35 --arch x86_64 --virttype kvm | virsh hypervisor-cpu-baseline --features /dev/stdin --machine q35 --arch x86_64 --virttype kvm > /var/lib/kubevirt-node-labeller/supported_features.xml