Introduce unmanaging servers into Mogan

In Pike release, Mogan has supported to manage existing bms,
in Queens release, Mogan will introduce unmanaging existing servers.
This function will help operator to release existing servers.

Change-Id: Ia7a4ff297ce44c482b11e057d60fc60299c29c27
Implements: bp unmanage-existing-bms

specs/queens/approved/unmanage-existing-bms.rst

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+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+=====================
+Unmanage Existing BMs
+=====================
+
+https://blueprints.launchpad.net/mogan/+spec/unmanage-existing-bms
+
+This spec is intended to allow mogan to unmanage nodes that have been managed
+into Mogan by operators or created by users.
+
+Problem description
+===================
+
+At present the mogan API can allow to manage nodes in active state which
+migrated to ironic by operators. This function will help operator to migrate
+running baremtal nodes from one "system" to another "system". But we also need
+the 'unmanage' function to help operator to release those nodes from Mogan
+under some cases, like be out of control from cloud system.
+
+Use Cases
+---------
+
+* As an operator of hybrid infrastructures, after managing running nodes
+  from base infrastructure to OpenStack cloud for a while, I want to release
+  those nodes from OpenStack cloud.
+
+* As an operator of multiple distinct OpenStack infrastructures, before
+  migrating running nodes from source OpenStack to destination OpenStack,
+  I want to release those nodes from this OpenStack.
+
+
+Proposed change
+===============
+
+*  Introduce a new API for unmanaging the managed server. Mogan will delete
+   the server object, including port/volume server association information.
+   But it will NOT delete the server from driver and keep the ports or volumes
+   in Neutron or Cinder since the baremetal node is still using by users.
+
+*  The taskflow will be like this::
+
+   #. User can specify the server id which will be unmanaged in unmanage API.
+   #. Mogan will check if the server is existing.
+   #. If it is existing, Mogan will remove the server object information from
+      DB, and update the quota of servers.
+   #. Mogan call Neutron API to update the device_id in port, change it from
+      server id to node id.
+   #. Since now cinder can't support to update the instance_id in volume,
+      Mogan will keep it in Cinder side.
+
+Alternatives
+------------
+
+None
+
+Data model impact
+-----------------
+
+None
+
+
+REST API impact
+---------------
+
+#. Add a new API to unmanage a server from Mogan, it is an admin only API::
+
+    DELETE v1/manageable_servers/{server_uuid}
+
+
+Security impact
+---------------
+
+None
+
+Notifications impact
+--------------------
+
+Notification about the unmanage action will be added.
+
+Other end user impact
+---------------------
+
+None
+
+Performance Impact
+------------------
+
+None
+
+Other deployer impact
+---------------------
+
+None
+
+Developer impact
+----------------
+
+None
+
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  wanghao <sxmatch1986@gmail.com>
+
+Work Items
+----------
+
+* Add new APIs.
+* Add a new taskflow which is described above for server unmanaging.
+* Add CLI support.
+
+Dependencies
+============
+
+None
+
+Testing
+=======
+
+Unit Testing will be added.
+
+Documentation Impact
+====================
+
+Docs about unmanaging servers will be added, including the API doc.
+
+References
+==========
+
+None