xenapi: log quality warning in init_host

The xenapi driver has not had working third party CI
for several months. As a result, this change logs a
warning on startup of the service in the init_host
method indicating the lack of testing and the possibility
that the driver may be deprecated in the future if the
situation does not change.

This was discussed at the 2019-05-30 nova meeting [1] and
also at the Train PTG.

[1] http://eavesdrop.openstack.org/meetings/nova/2019/nova.2019-05-30-14.00.log.html

Change-Id: I7f8eb7d5c5a9b1cb0a8d5e607d719b49a22675d3

nova/virt/xenapi/driver.py

@@ -118,6 +118,12 @@ def host_state(self):
         return self._host_state
 
     def init_host(self, host):
+        # TODO(mriedem): Consider deprecating the driver if there is still no
+        # working 3rd party CI by the end of the Train release.
+        LOG.warning('The xenapi driver is not tested by the OpenStack '
+                    'project and thus its quality can not be ensured. The '
+                    'driver may be deprecated in the future.')
+
         if CONF.xenserver.independent_compute:
             # Check various options are in the correct state:
             if CONF.xenserver.check_host: