test: stop firewall as first operation in cockpit-machines tests

Otherwise on fedora-35 we might get errors like:
error: internal error: Failed to apply firewall rules /usr/sbin/iptables
-w --table filter --insert LIBVIRT_INP --in-interface virbr0 --protocol
tcp --destination-port 67 --jump ACCEPT: iptables: No chain/target/match by that name.

test/machineslib.py

@@ -198,6 +198,9 @@ def setUp(self):
             # https://bugs.launchpad.net/ubuntu/+source/libvirt-dbus/+bug/1892757
             m.execute("usermod -a -G libvirt libvirtdbus")
 
+        # we don't have configuration to open the firewall for local libvirt machines, so just stop firewalld
+        m.execute("systemctl stop firewalld")
+
         self.startLibvirt()
         self.addCleanup(m.execute, f"systemctl stop {self.getLibvirtServiceName()}")
 
@@ -216,9 +219,6 @@ def setUp(self):
         # Stop all networks
         self.addCleanup(m.execute, "for n in $(virsh net-list --all --name); do virsh net-destroy $n || true; done")
 
-        # we don't have configuration to open the firewall for local libvirt machines, so just stop firewalld
-        m.execute(f"systemctl stop firewalld; systemctl reset-failed {self.getLibvirtServiceName()}; systemctl try-restart {self.getLibvirtServiceName()}")
-
         # user libvirtd instance tends to SIGABRT with "Failed to find user record for uid .." on shutdown during cleanup
         # so make sure that there are no leftover user processes that bleed into the next test
         self.addCleanup(self.machine.execute, '''pkill -u admin; while [ -n "$(pgrep -au admin | grep -v 'systemd --user')" ]; do sleep 0.5; done''')