Fix sample configuration generation for compute-related options

Currently the compute_opts are duplicated in both [DEFAULT] and [compute]
sections, while compute_group_opts are missing at all.

This patch does not affect where the options actually are, only where
they are displayed in the sample configuration.

Closes-Bug: #1712855

Change-Id: I68f246998fd68e669b0d9ef34b00ed384f4f0c90

nova/conf/compute.py

@@ -1138,4 +1138,4 @@ def register_opts(conf):
 
 def list_opts():
     return {'DEFAULT': ALL_OPTS,
-            'compute': compute_opts}
+            'compute': compute_group_opts}