fmf: Show "virt-host-validate qemu" in logs

This is an useful initial self-test. In RHEL 9.5 on TF it seems to have
lost "Checking for hardware virtualization", so let's see what's going
on.

This command usually exits with non-zero on TF machines as they don't
have /dev/kvm, so guard for that.

test/browser/browser.sh

@@ -26,6 +26,9 @@ fi
 rpm -q selinux-policy cockpit-bridge cockpit-machines
 rpm -qa | grep -E 'virt|qemu' | sort
 
+# basic libvirt selftests
+virt-host-validate qemu || echo "failed with code $?"
+
 # allow test to set up things on the machine
 mkdir -p /root/.ssh
 curl https://raw.githubusercontent.com/cockpit-project/bots/main/machine/identity.pub  >> /root/.ssh/authorized_keys