Update quota known issues docs

This removes the old reference to the nova-manage
command to refresh quota usage which no longer
applies since we started counting quotas in the
Pike release.

This replaces with a reference to the down-cell
known issue for counting quotas.

Change-Id: I2765f3ca3dc95345d4e4c4db43ac3dff4a509259

Author: mriedem

doc/source/admin/cells.rst

@@ -57,7 +57,7 @@ for details on command usage.
 Known issues
 ~~~~~~~~~~~~
 
-#. **Services and Performance:** In case a cell is down during the startup of nova
+1. **Services and Performance:** In case a cell is down during the startup of nova
    services, there is the chance that the services hang because of not being able
    to connect to all the cell databases that might be required for certain calculations
    and initializations. An example scenario of this situation is if
@@ -73,7 +73,9 @@ Known issues
    "slowness" may be experienced in operations requiring hitting all the cells
    because of the aforementioned configurable timeout/retry values.
 
-#. **Counting Quotas:** Another known issue is in the current approach of counting
+.. _cells-counting-quotas:
+
+2. **Counting Quotas:** Another known issue is in the current approach of counting
    quotas where we query each cell database to get the used resources and aggregate
    them which makes it sensitive to temporary cell outages. While the cell is
    unavailable, we cannot count resource usage residing in that cell database and

doc/source/user/quotas.rst

@@ -60,6 +60,7 @@ checks are made in order:
    the database manually as there is no REST API for removing quota class
    values from the database.
 
+.. _quota-usage-from-placement:
 
 Quota usage from placement
 ==========================
@@ -124,10 +125,9 @@ placement:
 Known issues
 ============
 
-TODO: talk about quotas getting out of sync and `how to recover`_
-
-.. _how to recover: https://specs.openstack.org/openstack/nova-specs/specs/newton/implemented/refresh-quotas-usage.html
-
+If not :ref:`counting quota usage from placement <quota-usage-from-placement>`
+it is possible for down or poor performing cells to impact quota calculations.
+See the :ref:`cells documentation <cells-counting-quotas>` for details.
 
 Future plans
 ============