Deprecate the powervm driver

As with the vmwareapi driver back in Ussuri [1], our indications suggest
that this driver is no longer maintained and may be abandonware. Start
the deprecation timer for the driver. If we see signs of life, we can
re-assess this decision.

[1] Ie39e9605dc8cebff3795a29ea91dc08ee64a21eb

Change-Id: Icdef0a03c3c6f56b08ec9685c6958d6917bc88cb

Author: stephenfin

nova/virt/powervm/driver.py

@@ -103,6 +103,14 @@ def init_host(self, host):
 
         Includes catching up with currently running VMs on the given host.
         """
+        LOG.warning(
+            'The powervm virt driver is deprecated and may be removed in a '
+            'future release. The driver is not tested by the OpenStack '
+            'project nor does it have clear maintainers and thus its quality'
+            'can not be ensured. If you are using the driver in production '
+            'please let us know the openstack-discuss mailing list or on IRC'
+        )
+
         # Build the adapter. May need to attempt the connection multiple times
         # in case the PowerVM management API service is starting.
         # TODO(efried): Implement async compute service enable/disable like

releasenotes/notes/deprecate-powervm-yoga-d368b43ba86eb830.yaml

@@ -0,0 +1,6 @@
+---
+deprecations:
+  - |
+    The powervm virt driver is deprecated and may be removed in a future
+    release. The driver is not tested by the OpenStack project nor does it have
+    clear maintainers and thus its quality can not be ensured.