copr-be: provide ssh key in config.iso drive for libvirt

This is the way to tell the instance's cloud-init what is the (currently
rotated) correct ssh pub key.

roles/copr/backend/templates/provision/libvirt-new

@@ -200,6 +200,21 @@ class LibvirtSpawner:
         """
 
         todo_files = copy.copy(self.config_files)
+
+        # Make sure the machine trusts our buildsys.pub key (via cloud-init).
+        with open("/var/lib/resallocserver/provision/files/buildsys.pub", "r",
+                  encoding='utf-8') as file:
+            public_key = file.read()
+
+        user_data = f"""\n
+#cloud-config
+ssh_authorized_keys:
+  - {public_key}
+"""
+        todo_files.append(ConfigFile('user-data', user_data))
+        meta_data = "instance-id: {self.vm_name}\n"
+        todo_files.append(ConfigFile('meta-data', meta_data))
+
         startup_script = self.get_startup_script()
         if startup_script:
             todo_files.append(startup_script)
@@ -216,9 +231,10 @@ class LibvirtSpawner:
 
         image = os.path.join(self.workdir, 'config.iso')
 
-        # The 'eimg_config' label is not important, we search for /dev/sr0
-        # anyway.
-        if self.call(['mkisofs', '-o', image, '-V', 'eimg_config', '-r', '-J',
+        # The 'cidata' label is important, otherwise cloud-init can't take the
+        # image as NoCloud drive.  Other files shouldn't be a problem for cloud
+        # init.
+        if self.call(['mkisofs', '-o', image, '-V', 'cidata', '-r', '-J',
                       '--quiet', config_dir]) != 0:
             raise Exception("mkisofs failed")
         return image