test: More precise firewall configuration

Only enable cockpit in the firewall if it is actually running, not
merely installed.

test/vm.install

@@ -7,7 +7,7 @@ set -eux
 mkdir -p /etc/cockpit
 printf "[WebService]\\nAllowUnencrypted=true\\n" > /etc/cockpit/cockpit.conf
 
-if type firewall-cmd >/dev/null 2>&1; then
+if systemctl is-active -q firewalld.service; then
     firewall-cmd --add-service=cockpit --permanent
 fi
 systemctl enable cockpit.socket