fix: add an authorization matrix test and close the endpoints it finds

Add webvirtcloud/test_authorization_matrix.py, which walks every named URL
and checks that a user without any VM/compute relation only reaches an
explicit allowlist, and that the global view_instances permission does not
open consoles. It found:

- /computes/<id>/... views without any check (compute_graph,
  get_compute_*, get_dom_capabilities, storages.get_volumes): the whole
  computes URL namespace is now wrapped with superuser_only, so a view
  added there later cannot be exposed by a missing decorator.
- guess_mac_address (leaks dhcpd.conf host/MAC pairs), random_mac_address
  and guess_clone_name: superuser-only, like the buttons that use them.
- check_instance: cross-tenant VM name lookup with no caller; removed.
- getvvfile and get_vdi_url: reachable with only view_instances, and the
  .vv file contains the VNC password.

Console access now follows one rule, instances.utils.can_open_console:
an active superuser or an active owner of the VM. The global
view_instances permission is read-only. It is used by the console page,
novncd, getvvfile and get_vdi_url (getvvfile and the VDI tab are kept for
virt-viewer users). The console page answers 403 instead of 500 when
access is denied, with the same answer for a missing VM.

instances/utils.py

@@ -14,6 +14,20 @@ from vrtManager.instance import wvmInstance, wvmInstances
 from .models import Instance
 
 
+def can_open_console(user, instance):
+    """
+    The single rule for console access (noVNC page, novncd, the virt-viewer
+    .vv file and the VDI URL): an active superuser or an active owner of the
+    VM. The global view_instances permission is read-only and does not grant
+    an interactive console (ROADMAP S-09).
+    """
+    if not user.is_active:
+        return False
+    if user.is_superuser:
+        return True
+    return UserInstance.objects.filter(instance=instance, user=user).exists()
+
+
 def get_clone_free_names(size=10):
     prefix = app_settings.CLONE_INSTANCE_DEFAULT_PREFIX
     free_names = []