docs: Add a new cells v2 document

We currently have three cells v2 documents in-tree:

- A 'user/cellsv2-layout' document that details the structure or
  architecture of a cells v2 deployment (which is to say, any modern
  nova deployment)
- A 'user/cells' document, which is written from a pre-cells v2
  viewpoint and details the changes that cells v2 *will* require and the
  benefits it *would* bring. It also includes steps for upgrading from
  pre-cells v2 (that is, pre-Pike) deployment or a deployment with cells
  v1 (which we removed in Train and probably broke long before)
- An 'admin/cells' document, which doesn't contain much other than some
  advice for handling down cells

Clearly there's a lot of cruft to be cleared out as well as some
centralization of information that's possible. As such, we combine all
of these documents into one document, 'admin/cells'. This is chosen over
'users/cells' since cells are not an end-user-facing feature. References
to cells v1 and details on upgrading from pre-cells v2 deployments are
mostly dropped, as are some duplicated installation/configuration steps.
Formatting is fixed and Sphinx-isms used to cross reference config
option where possible. Finally, redirects are added so that people can
continue to find the relevant resources. The result is (hopefully) a
one stop shop for all things cells v2-related that operators can use to
configure and understand their deployments.

Change-Id: If39db50fd8b109a5a13dec70f8030f3663555065
Signed-off-by: Stephen Finucane <[email protected]>

Author: stephenfin

doc/source/_extra/.htaccess

@@ -9,12 +9,12 @@ redirectmatch 301 ^/nova/([^/]+)/api_plugins.html$ /nova/$1/contributor/api.html
 redirectmatch 301 ^/nova/([^/]+)/architecture.html$ /nova/$1/user/architecture.html
 redirectmatch 301 ^/nova/([^/]+)/block_device_mapping.html$ /nova/$1/user/block-device-mapping.html
 redirectmatch 301 ^/nova/([^/]+)/blueprints.html$ /nova/$1/contributor/blueprints.html
-redirectmatch 301 ^/nova/([^/]+)/cells.html$ /nova/$1/user/cells.html
+redirectmatch 301 ^/nova/([^/]+)/cells.html$ /nova/$1/admin/cells.html
 redirectmatch 301 ^/nova/([^/]+)/code-review.html$ /nova/$1/contributor/code-review.html
 redirectmatch 301 ^/nova/([^/]+)/conductor.html$ /nova/$1/user/conductor.html
 redirectmatch 301 ^/nova/([^/]+)/development.environment.html$ /nova/$1/contributor/development-environment.html
 redirectmatch 301 ^/nova/([^/]+)/devref/api.html /nova/$1/contributor/api.html
-redirectmatch 301 ^/nova/([^/]+)/devref/cells.html /nova/$1/user/cells.html
+redirectmatch 301 ^/nova/([^/]+)/devref/cells.html /nova/$1/admin/cells.html
 redirectmatch 301 ^/nova/([^/]+)/devref/filter_scheduler.html /nova/$1/admin/scheduling.html
 # catch all, if we hit something in devref assume it moved to
 # reference unless we have already triggered a hit above.
@@ -64,7 +64,9 @@ redirectmatch 301 ^/nova/([^/]+)/testing/zero-downtime-upgrade.html$ /nova/$1/co
 redirectmatch 301 ^/nova/([^/]+)/threading.html$ /nova/$1/reference/threading.html
 redirectmatch 301 ^/nova/([^/]+)/upgrade.html$ /nova/$1/admin/upgrades.html
 redirectmatch 301 ^/nova/([^/]+)/user/aggregates.html$ /nova/$1/admin/aggregates.html
-redirectmatch 301 ^/nova/([^/]+)/user/cellsv2_layout.html$ /nova/$1/user/cellsv2-layout.html
+redirectmatch 301 ^/nova/([^/]+)/user/cells.html$ /nova/$1/admin/cells.html
+redirectmatch 301 ^/nova/([^/]+)/user/cellsv2-layout.html$ /nova/$1/admin/cells.html
+redirectmatch 301 ^/nova/([^/]+)/user/cellsv2_layout.html$ /nova/$1/admin/cells.html
 redirectmatch 301 ^/nova/([^/]+)/user/config-drive.html$ /nova/$1/user/metadata.html
 redirectmatch 301 ^/nova/([^/]+)/user/filter-scheduler.html$ /nova/$1/admin/scheduling.html
 redirectmatch 301 ^/nova/([^/]+)/user/metadata-service.html$ /nova/$1/user/metadata.html