Fix issue moving hosts back to freepool

If an aggregate fails to be created for some reason, for example because
the requested node is not in the freepool, some cleanup occurs. Part of
the cleanup is ensuring the target node is moved _back_ to the freepool.
This should theoretically "heal" cases where the node wasn't in the
freepool but also wasn't in some lease aggregate.

However, this call to Nova's API refers to the freepool aggregate by its
name, which is not supported here: the ID must be used[1]. This caused
this operation to fail and raise a NotFound, confusingly (because Nova
couldn't find an aggregate with ID='freepool' for example.)

[1]:
https://docs.openstack.org/api-ref/compute/?expanded=add-host-detail#add-host

Closes-Bug: #1847821
Change-Id: I7af4d407b183578617131f0de42becb3dc2bc415

blazar/tests/utils/openstack/test_nova.py

@@ -347,8 +347,8 @@ class ReservationPoolTestCase(tests.TestCase):
         check0 = self.nova.aggregates.add_host
         check0.assert_has_calls([mock.call(self.fake_aggregate.id, 'host1'),
                                  mock.call(self.fake_aggregate.id, 'host2'),
-                                 mock.call('freepool', 'host1'),
-                                 mock.call('freepool', 'host2')])
+                                 mock.call(self.fake_freepool.id, 'host1'),
+                                 mock.call(self.fake_freepool.id, 'host2')])
         check1 = self.nova.aggregates.remove_host
         check1.assert_has_calls([mock.call(self.fake_freepool.id, 'host1'),
                                  mock.call(self.fake_freepool.id, 'host2'),

blazar/utils/openstack/nova.py

@@ -387,7 +387,7 @@ class ReservationPool(NovaClientWrapper):
             if removed_hosts:
                 LOG.warn('Adding hosts back to freepool: %s', removed_hosts)
                 for host in removed_hosts:
-                    self.nova.aggregates.add_host(freepool_agg.name, host)
+                    self.nova.aggregates.add_host(freepool_agg.id, host)
             raise e
 
         return self.get_aggregate_from_name_or_id(pool)

releasenotes/notes/bug-1847821-2f9d6e61f438dc4f.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Updates the on_start failure handlers to look up the freepool aggregate by
+    ID, not by name, when moving hosts back to the freepool. Fixes issue where
+    hosts wind up without any aggregate during lease start failure.  For more
+    details, see `bug 1847821
+    <https://bugs.launchpad.net/blazar/+bug/1847821>`_.