kvm: Hold start until images are ready

This will minimise amount of needless restarts.

software/kvm/buildout.hash.cfg

@@ -55,7 +55,7 @@ md5sum = b7e87479a289f472b634a046b44b5257
 
 [template-kvm-run]
 filename = template/template-kvm-run.in
-md5sum = 2909821e8eebfe8928a0a0cfb94c0348
+md5sum = b8cc7c76438212e0522ebede88649393
 
 [template-kvm-controller]
 filename = template/kvm-controller-run.in

software/kvm/template/template-kvm-run.in

@@ -361,6 +361,9 @@ else:
             '-drive',
             'file=%s,media=cdrom' % (link,)
           ])
+    else:
+      raise ValueError('boot-image-url-select not ready yet')
+
   if boot_image_url_list_json_config:
     # Support boot-image-url-list
     with open(boot_image_url_list_json_config) as fh:
@@ -373,6 +376,8 @@ else:
             '-drive',
             'file=%s,media=cdrom' % (link,)
           ])
+    else:
+      raise ValueError('boot-image-url-list not ready yet')
   # Always add by default the default image
   kvm_argument_list.extend([
       '-drive', 'file=%s,media=cdrom' % default_cdrom_iso