Use random hostname starting with xcp-ng-

This allows to have different hostname when installing new VM.

scripts/install_xcpng.py

@@ -4,7 +4,9 @@
 import atexit
 import logging
 import os
+import random
 import requests
+import string
 import subprocess
 import sys
 import tempfile
@@ -47,6 +49,9 @@ def generate_answerfile(directory, installer, hostname_or_ip, action, hdd):
     cmd = ['openssl', 'passwd', '-6', password]
     res = subprocess.run(cmd, stdout=subprocess.PIPE)
     encrypted_password = res.stdout.decode().strip()
+    hostname = "xcp-ng-" + "".join(
+        random.choice(string.ascii_lowercase) for i in range(5)
+    )
     with open(f'{directory}/answerfile.xml', 'w') as answerfile:
         if action == 'install':
             answerfile.write(f"""<?xml version="1.0"?>
@@ -58,6 +63,7 @@ def generate_answerfile(directory, installer, hostname_or_ip, action, hdd):
     <source type="url">{installer}</source>
     <admin-interface name="eth0" proto="dhcp" />
     <timezone>Europe/Paris</timezone>
+    <hostname>{hostname}</hostname>
     <script stage="filesystem-populated" type="url">
         http://{pxe}/configs/presets/scripts/filesystem-populated.py
     </script>