Add troubleshooting item about ignored microversions

If the compute endpoint in the service catalog is configured
for /v2 legacy compat mode, microversions in the request are
silently ignored by the LegacyV2CompatibleWrapper. This
adds a troubleshooting entry for that situation.

At this point, we might want to consider deprecating or at
least logging warnings if microversions are requested and
LegacyV2CompatibleWrapper strips them out, but that's fodder
for a separate change.

Change-Id: Ia7ecbf95d0a3e14c7f82b6a93c2ac4c4cfb89549

doc/source/admin/support-compute.rst

@@ -423,3 +423,29 @@ Install the ``sg3-utils`` package on the compute node. For example:
 .. code-block:: console
 
    # apt-get install sg3-utils
+
+Requested microversions are ignored
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Problem
+-------
+
+When making a request with a microversion beyond 2.1, for example:
+
+.. code-block:: console
+
+  $ openstack --os-compute-api-version 2.15 server group create \
+    --policy soft-anti-affinity my-soft-anti-group
+
+It fails saying that "soft-anti-affinity" is not a valid policy, even
+thought it is allowed with the `2.15 microversion`_.
+
+.. _2.15 microversion: https://docs.openstack.org/nova/latest/reference/api-microversion-history.html#id13
+
+Solution
+--------
+
+Ensure the ``compute`` endpoint in the identity service catalog is pointing
+at ``/v2.1`` instead of ``/v2``. The former route supports microversions,
+while the latter route is considered the legacy v2.0 compatibility-mode
+route which renders all requests as if they were made on the legacy v2.0 API.