Two testcases are executed consecutively:
test_create_second_image_when_first_image_is_being_saved and
test_delete_image_that_is_not_yet_active
In the first, the image created from a certain instance gets active, but the instance remains in uploading status. When the next testcase comes to be executed, it tries to create another snapshot from the uploading image and causes an error

My suggestion here is to wait for the instance to become available before trying to create the snapshot in the second testcase.

The logs on n-api related to that:

2013-08-29 13:03:06.331 DEBUG nova.api.openstack.wsgi [req-68611dfc-e6ab-4f27-a813-dd97baab4878 ImagesOneServerTestXML256228464-user ImagesOneServerTestXML954616129-tenant] No Content-Type provided in request get_body /opt/stack/new/nova/nova/api/openstack/wsgi.py:801
2013-08-29 13:03:06.331 DEBUG nova.api.openstack.wsgi [req-68611dfc-e6ab-4f27-a813-dd97baab4878 ImagesOneServerTestXML256228464-user ImagesOneServerTestXML954616129-tenant] Calling method <bound method Controller.delete of <nova.api.openstack.compute.servers.Controller object at 0x47cc450>> _process_stack /opt/stack/new/nova/nova/api/openstack/wsgi.py:928
2013-08-29 13:03:06.368 DEBUG nova.compute.api [req-68611dfc-e6ab-4f27-a813-dd97baab4878 ImagesOneServerTestXML256228464-user ImagesOneServerTestXML954616129-tenant] [instance: 476fc5e9-e5b5-468f-a744-145837dfc7e2] Going to try to terminate instance delete /opt/stack/new/nova/nova/compute/api.py:1465
2013-08-29 13:03:06.429 DEBUG nova.quota [req-68611dfc-e6ab-4f27-a813-dd97baab4878 ImagesOneServerTestXML256228464-user ImagesOneServerTestXML954616129-tenant] Created reservations ['0454632b-10e4-4f56-934f-5fcb16982e53', '55a79376-c1b9-48c5-b7d4-af3ef4950f4a', 'a7e219c5-9eb3-4bbe-a6ae-a7cee63d3d78'] reserve /opt/stack/new/nova/nova/quota.py:1256
2013-08-29 13:03:06.438 DEBUG nova.servicegroup.api [req-68611dfc-e6ab-4f27-a813-dd97baab4878 ImagesOneServerTestXML256228464-user ImagesOneServerTestXML954616129-tenant] Check if the given member [<nova.db.sqlalchemy.models.Service object at 0x7a16f90>] is part of the ServiceGroup, is up service_is_up /opt/stack/new/nova/nova/servicegroup/api.py:94
2013-08-29 13:03:06.439 DEBUG nova.servicegroup.drivers.db [req-68611dfc-e6ab-4f27-a813-dd97baab4878 ImagesOneServerTestXML256228464-user ImagesOneServerTestXML954616129-tenant] DB_Driver.is_up last_heartbeat = 2013-08-29 13:02:59 elapsed = 7.439029 is_up /opt/stack/new/nova/nova/servicegroup/drivers/db.py:67
2013-08-29 13:03:06.442 DEBUG nova.openstack.common.rpc.amqp [req-68611dfc-e6ab-4f27-a813-dd97baab4878 ImagesOneServerTestXML256228464-user ImagesOneServerTestXML954616129-tenant] Making asynchronous cast on compute.devstack-precise-hpcloud-az3-190744... cast /opt/stack/new/nova/nova/openstack/common/rpc/amqp.py:542
2013-08-29 13:03:06.442 DEBUG nova.openstack.common.rpc.amqp [req-68611dfc-e6ab-4f27-a813-dd97baab4878 ImagesOneServerTestXML256228464-user ImagesOneServerTestXML954616129-tenant] UNIQUE_ID is 0d6d5d3ba5624a4087a3f9d641225a08. _add_unique_id /opt/stack/new/nova/nova/openstack/common/rpc/amqp.py:322
2013-08-29 13:03:06.444 23111 DEBUG amqp [-] Closed channel #1 _do_close /usr/local/lib/python2.7/dist-packages/amqp/channel.py:88
2013-08-29 13:03:06.444 23111 DEBUG amqp [-] using channel_id: 1 __init__ /usr/local/lib/python2.7/dist-packages/amqp/channel.py:70
2013-08-29 13:03:06.445 23111 DEBUG amqp [-] Channel open _open_ok /usr/local/lib/python2.7/dist-packages/amqp/channel.py:420
2013-08-29 13:03:06.446 INFO nova.osapi_compute.wsgi.server [req-68611dfc-e6ab-4f27-a813-dd97baab4878 ImagesOneServerTestXML256228464-user ImagesOneServerTestXML954616129-tenant] 127.0.0.1 "DELETE /v2/ed550a8568114662afd0e3f3e808c8e5/servers/476fc5e9-e5b5-468f-a744-145837dfc7e2 HTTP/1.1" status: 204 len: 198 time: 0.1169958