Fix and update compute schedulers config guide

There were several things wrong with this doc since the migration
in-tree in pike, which are handled here:

- Updated options to use the current names.
- Any mention of the periodic_task_interval option is removed
  since this doc is really about the FilterScheduler, and the
  periodic task interval is only used by the CachingScheduler to
  cache and refresh hosts, something the FilterScheduler doesn't do.
  The note about service_down_time is already covered in the help
  text for the periodic_task_interval option.
- Removed a broken (and oddly placed) link to the block storage
  docs; it's unclear why the compute scheduler docs need to randomly
  link to the block storage docs for schedluing (maybe that was
  super legacy from the nova-volume days).
- Fixed a broken link to the 'evacuate instances' docs.

This change does not get into details for the individual filters
or weighers, only the overview and filter scheduler description.

Change-Id: Ie5bb9781e1997ad12521b5df5245a78b587a4a20
Closes-Bug: #1749235

doc/source/admin/configuration/schedulers.rst

@@ -13,12 +13,14 @@ Compute is configured with the following default scheduler options in the
 
 .. code-block:: ini
 
-   scheduler_driver_task_period = 60
-   scheduler_driver = nova.scheduler.filter_scheduler.FilterScheduler
-   scheduler_available_filters = nova.scheduler.filters.all_filters
-   scheduler_default_filters = RetryFilter, AvailabilityZoneFilter, ComputeFilter, ComputeCapabilitiesFilter, ImagePropertiesFilter, ServerGroupAntiAffinityFilter, ServerGroupAffinityFilter
+   [scheduler]
+   driver = filter_scheduler
 
-By default, the ``scheduler_driver`` is configured as a filter scheduler, as
+   [filter_scheduler]
+   available_filters = nova.scheduler.filters.all_filters
+   enabled_filters = RetryFilter, AvailabilityZoneFilter, ComputeFilter, ComputeCapabilitiesFilter, ImagePropertiesFilter, ServerGroupAntiAffinityFilter, ServerGroupAffinityFilter
+
+By default, the scheduler ``driver`` is configured as a filter scheduler, as
 described in the next section. In the default configuration, this scheduler
 considers hosts that meet all the following criteria:
 
@@ -39,29 +41,13 @@ considers hosts that meet all the following criteria:
 
 * Are in a set of group hosts (if requested) (``ServerGroupAffinityFilter``).
 
-The scheduler caches its list of available hosts; use the
-``scheduler_driver_task_period`` option to specify how often the list is
-updated.
-
-.. note::
-
-   Do not configure ``service_down_time`` to be much smaller than
-   ``scheduler_driver_task_period``; otherwise, hosts appear to be dead while
-   the host list is being cached.
-
-For information about the volume scheduler, see the `Block Storage section
-<https://docs.openstack.org/admin-guide/blockstorage-manage-volumes.html>`_ of
-OpenStack Administrator Guide.
-
 The scheduler chooses a new host when an instance is migrated.
 
 When evacuating instances from a host, the scheduler service honors the target
 host defined by the administrator on the :command:`nova evacuate` command.  If
 a target is not defined by the administrator, the scheduler determines the
-target host. For information about instance evacuation, see `Evacuate instances
-<https://docs.openstack.org/admin-guide/
-compute-node-down.html#evacuate-instances>`_ section of the OpenStack
-Administrator Guide.
+target host. For information about instance evacuation, see
+:ref:`Evacuate instances <node-down-evacuate-instances>`.
 
 .. _compute-scheduler-filters:
 
@@ -84,14 +70,15 @@ request, described in the :ref:`weights` section.
 
 .. figure:: /figures/filteringWorkflow1.png
 
-The ``scheduler_available_filters`` configuration option in ``nova.conf``
-provides the Compute service with the list of the filters that are used by the
-scheduler. The default setting specifies all of the filter that are included
-with the Compute service:
+The ``available_filters`` configuration option in ``nova.conf``
+provides the Compute service with the list of the filters that are available
+for use by the scheduler. The default setting specifies all of the filters that
+are included with the Compute service:
 
 .. code-block:: ini
 
-   scheduler_available_filters = nova.scheduler.filters.all_filters
+   [filter_scheduler]
+   available_filters = nova.scheduler.filters.all_filters
 
 This configuration option can be specified multiple times.  For example, if you
 implemented your own custom filter in Python called ``myfilter.MyFilter`` and
@@ -100,16 +87,18 @@ you wanted to use both the built-in filters and your custom filter, your
 
 .. code-block:: ini
 
-   scheduler_available_filters = nova.scheduler.filters.all_filters
-   scheduler_available_filters = myfilter.MyFilter
+   [filter_scheduler]
+   available_filters = nova.scheduler.filters.all_filters
+   available_filters = myfilter.MyFilter
 
-The ``scheduler_default_filters`` configuration option in ``nova.conf`` defines
+The ``enabled_filters`` configuration option in ``nova.conf`` defines
 the list of filters that are applied by the ``nova-scheduler`` service. The
 default filters are:
 
 .. code-block:: ini
 
-   scheduler_default_filters = RetryFilter, AvailabilityZoneFilter, ComputeCapabilitiesFilter, ImagePropertiesFilter, ServerGroupAntiAffinityFilter, ServerGroupAffinityFilter
+   [filter_scheduler]
+   enabled_filters = RetryFilter, AvailabilityZoneFilter, ComputeCapabilitiesFilter, ImagePropertiesFilter, ServerGroupAntiAffinityFilter, ServerGroupAffinityFilter
 
 Compute filters
 ~~~~~~~~~~~~~~~

doc/source/admin/node-down.rst

@@ -5,6 +5,8 @@ Recover from a failed compute node
 If you deploy Compute with a shared file system, you can use several methods to
 quickly recover from a node failure. This section discusses manual recovery.
 
+.. _node-down-evacuate-instances:
+
 Evacuate instances
 ~~~~~~~~~~~~~~~~~~