Fix configure-vm.py and xml file for centos8

Fixing configure-vm script and vm.xml with this patch because for
latest OS like centos8 - older python version and older qemu machine
type is causing issue.

* For configure-vm.py - Replacing python with python3 in environment
path as python3 is the default in many latest OS.

* For vm.xml - Replacing Machine type from pc-1.0 to pc.
- pc-1.0 is old and unsupported machine type for Centos8
- Moving machine type from pc-1.0 to pc will help as pc have alias to
supported qemu machine type

Related-Bug: #1875681
Change-Id: Icd7e98ceb8859f730a32981a150f2730bde9836b

devstack/tools/ironic/scripts/configure-vm.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 #    Licensed under the Apache License, Version 2.0 (the "License"); you may
 #    not use this file except in compliance with the License. You may obtain

devstack/tools/ironic/templates/vm.xml

@@ -3,7 +3,7 @@
   <memory unit='KiB'>{{ memory }}</memory>
   <vcpu>{{ cpus }}</vcpu>
   <os>
-    <type arch='{{ arch }}' machine='pc-1.0'>hvm</type>
+    <type arch='{{ arch }}' machine='pc'>hvm</type>
     {% if bootdev == 'network' and not uefi_loader %}
     <boot dev='{{ bootdev }}'/>
     {% endif %}