[Nova] Artifacts after instance resizing

Detailed bug description:
Resize operation finished but some files were not deleted from original node.
Steps to reproduce:
1)Deploy cluster
[root@nailgun ~]# fuel node
id | status | name | cluster | ip | mac | roles | pending_roles | online | group_id
---|----------|------------------|---------|-------------|-------------------|-----------------|---------------|--------|---------
2 | ready | Untitled (fa:2c) | 1 | 10.109.5.5 | 64:98:71:73:fa:2c | controller | | True | 1
1 | ready | Untitled (96:6b) | 1 | 10.109.5.3 | 64:b1:ec:a2:96:6b | controller | | True | 1
3 | ready | Untitled (fa:f4) | 1 | 10.109.5.6 | 64:33:ed:44:fa:f4 | controller | | True | 1
4 | ready | Untitled (78:ad) | 1 | 10.109.5.7 | 64:b4:77:d3:78:ad | cinder, compute | | True | 1
5 | ready | Untitled (00:48) | 1 | 10.109.5.4 | 64:b4:b3:c8:00:48 | cinder, compute | | True | 1

2) Launch 2 instances based on TestVM with micro flavor
root@node-5:~# ll /var/lib/nova/instances/
total 4
drwxr-xr-x 6 nova nova 136 May 23 10:37 ./
drwxr-xr-x 10 nova nova 105 May 17 06:25 ../
drwxr-xr-x 2 nova nova 22 May 23 10:37 15fa17ba-a89b-4fa2-b844-6f7d8d613fa9/
drwxr-xr-x 2 nova nova 69 May 23 10:36 67bb6d46-a99d-42e3-9fff-eba3d7965226/
drwxr-xr-x 2 nova nova 53 May 23 10:02 _base/
-rw-r--r-- 1 nova nova 47 May 23 10:02 compute_nodes
drwxr-xr-x 2 nova nova 91 May 23 10:02 locks/

3) Run instance resizing to "small"
4) Check target node (4). New dir should be created.
5) Check base node (5). Old dir still exist:
root@node-5:~# ll /var/lib/nova/instances/15fa17ba-a89b-4fa2-b844-6f7d8d613fa9/
total 4
drwxr-xr-x 2 nova nova 22 May 23 10:37 ./
drwxr-xr-x 6 nova nova 136 May 23 10:37 ../
-rw-r--r-- 1 nova nova 79 May 23 10:37 disk.info
root@node-5:~# cat /var/lib/nova/instances/15fa17ba-a89b-4fa2-b844-6f7d8d613fa9/disk.info
{"/var/lib/nova/instances/15fa17ba-a89b-4fa2-b844-6f7d8d613fa9/disk": "qcow2"}
root@node-5:~#
6) Delete instance. Dir and file were not deleted.

Expected results:
All instance files should be deleted

Actual result:
Some files are not deleted after migration

Reproducibility:
yes

Workaround:
operators can remove the files manually

Impact:
Medium (only QCOW2/RAW ephemerals must be affected, while RBD is the recommend way to deploy Nova)

Description of the environment:
Basic env from Fuel unit test

[root@nailgun ~]# shotgun2 short-report
cat /etc/fuel_build_id:
 324
cat /etc/fuel_build_number:
 324
cat /etc/fuel_release:
 9.0
cat /etc/fuel_openstack_version:
 mitaka-9.0

Additional information:
May be there is some correlation with
https://bugs.launchpad.net/nova/+bug/1548450