authz: add QAuthZList object type for an access control list

authz: add QAuthZList object type for an access control list

Add a QAuthZList object type that implements the QAuthZ interface. This
built-in implementation maintains a trivial access control list with a
sequence of match rules and a final default policy. This replicates the
functionality currently provided by the qemu_acl module.

To create an instance of this object via the QMP monitor, the syntax
used would be:

  {
    "execute": "object-add",
    "arguments": {
      "qom-type": "authz-list",
      "id": "authz0",
      "props": {
        "rules": [
           { "match": "fred", "policy": "allow", "format": "exact" },
           { "match": "bob", "policy": "allow", "format": "exact" },
           { "match": "danb", "policy": "deny", "format": "glob" },
           { "match": "dan*", "policy": "allow", "format": "exact" },
        ],
        "policy": "deny"
      }
    }
  }

This sets up an authorization rule that allows 'fred', 'bob' and anyone
whose name starts with 'dan', except for 'danb'. Everyone unmatched is
denied.

It is not currently possible to create this via -object, since there is
no syntax supported to specify non-scalar properties for objects. This
is likely to be addressed by later support for using JSON with -object,
or an equivalent approach.

In any case the future "authz-listfile" object can be used from the
CLI and is likely a better choice, as it allows the ACL to be refreshed
automatically on change.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>