fix(instances): a new VM and each clone get a VNC password of their own

Since the VM create became a job (6f0c7300) every new VM was defined with
no VNC password, and a clone copied its source's password (or its lack
of one) exactly: every clone of a template shared it. Computes listen
for VNC on all their addresses (dev/libvirt-bootstrap.sh), so anyone who
could reach a compute's VNC ports opened any of these consoles directly,
without the panel; the README's firewall rule was the only guard.

The create job asks for create.py's random 8-character password again,
and a clone's VNC graphics get a new random one. The console page sends
the password to a user with passwordless_console, which the user create
form now ticks by default next to change_password; a user without it is
asked for the password, as the permission intends. Existing VMs keep
their settings.

Live create, clone and VM page tests pass on a TCP compute.

vrtManager/instance.py

@@ -2398,6 +2398,10 @@ class wvmInstance(wvmConnect):
                 raise ValueError(f"No MAC address for network interface {num}")
             net.find("mac").set("address", self.fix_mac(mac))
 
+        # the clone's console gets a password of its own: one copied from the source would open both
+        for graphics in tree.findall("devices/graphics[@type='vnc']"):
+            graphics.set("passwd", util.randomPasswd(8))  # the length VNC allows
+
         nvram = tree.find("os/nvram")
         if nvram is not None and nvram.get("type", "file") != "file":
             raise util.OperationError(gettext_noop("Cannot clone a VM whose NVRAM is not a file"))

vrtManager/tests/test_clone_console.py

@@ -0,0 +1,26 @@
+"""A clone's VNC console gets a password of its own: one copied from its
+source (a template's, say) would open the source's and every other clone's."""
+
+import unittest
+
+from vrtManager.instance import wvmInstance
+
+
+def clone_graphics(passwd_attribute):
+    p = wvmInstance.__new__(wvmInstance)  # no connection: only these calls
+    p.get_instances = lambda: []
+    p._XMLDesc = lambda flags: f"""<domain><name>tpl</name><uuid>u</uuid><devices>
+        <graphics type='vnc' port='-1' autoport='yes' {passwd_attribute} listen='0.0.0.0'/></devices></domain>"""
+    tree, _ = p._clone_definition({"name": "copy"}, "abababab-0000-1111-2222-333333333333")
+    return tree.find("devices/graphics")
+
+
+class CloneConsoleTestCase(unittest.TestCase):
+    def test_each_clone_gets_its_own_vnc_password(self):
+        passwords = {clone_graphics("passwd='shared12'").get("passwd") for _ in range(5)}
+        self.assertNotIn("shared12", passwords)
+        self.assertEqual(len(passwords), 5)
+        self.assertTrue(all(len(p) == 8 for p in passwords))  # the length VNC allows
+
+    def test_a_source_without_a_password_gives_a_clone_with_one(self):
+        self.assertEqual(len(clone_graphics("").get("passwd")), 8)