Deprecate compute options

Marked following config options as deprecated:
1. multi_instance_display_name_template
2. null_kernel

API behaviour should not be changed through these flags and these
value should be hard coded.

Blueprint centralize-config-options-ocata

Change-Id: I613be6a42b3f2163fc7aa10f40b1a087306f89dd

nova/conf/compute.py

@@ -65,9 +65,16 @@ Possible values:
   doesn't need them.
 * Default list: ['cache_in_nova', 'bittorrent']
 """),
-    # TODO(aunnam): This option needs to be deprecated
     cfg.StrOpt('null_kernel',
         default='nokernel',
+        deprecated_for_removal=True,
+        deprecated_since='15.0.0',
+        deprecated_reason="""
+When an image is booted with the property 'kernel_id' with the value
+'nokernel', Nova assumes the image doesn't require an external kernel and
+ramdisk. This option allows user to change the API behaviour which should not
+be allowed and this value "nokernel" should be hard coded.
+""",
         help="""
 This option is used to decide when an image should have no external
 ramdisk or kernel. By default this is set to 'nokernel', so when an
@@ -75,9 +82,14 @@ image is booted with the property 'kernel_id' with the value
 'nokernel', Nova assumes the image doesn't require an external kernel
 and ramdisk.
 """),
-    # TODO(aunnam): This option needs to be deprecated
     cfg.StrOpt('multi_instance_display_name_template',
         default='%(name)s-%(count)d',
+        deprecated_for_removal=True,
+        deprecated_since='15.0.0',
+        deprecated_reason="""
+This config changes API behaviour. All changes in API behaviour should be
+discoverable.
+""",
         help="""
 When creating multiple instances with a single request using the
 os-multiple-create API extension, this template will be used to build

releasenotes/notes/deprecate-compute-options-011c9a454182a8bf.yaml

@@ -0,0 +1,7 @@
+---
+deprecations:
+  - |
+    The config options ``multi_instance_display_name_template`` and
+    ``null_kernel`` in the ``DEFAULT`` group are now deprecated and may be
+    removed as early as the 16.0.0 release. These options are deprecated to
+    keep API behaviour consistent across deployments.