Bug 1885286

Description of problem:

serial execution of playbook ovirt-ova-export, olso when running on different datacenters/hosts



Steps to Reproduce:
execute multiple "export to ova" at the same time

Actual results:

the export are executed in serial

Expected results:

the export are executed in parallel

Additional info:
as in https://bugzilla.redhat.com/show_bug.cgi?id=1855782:

If you run export_vm_as_ova.py for vm1 and then for vm2 after one minute, they both to start initially as jobs, but actually the "qemu-img convert" process for the second vm doesn't start until the first one has completed.
Eg in engine events you see 
Starting to export Vm c8server as a Virtual Appliance 10/2/202:50:23 PM
Starting to export Vm c8client as a Virtual Appliance 10/2/202:51:41 PM
but only when the first one completes, you see on host that after that the qemu-img process for the second one start.

I see that the derived ansible job on engine, named "/usr/share/ovirt-engine/playbooks/ovirt-ova-export.yml" and executed as this command:

ovirt     9534  1642  6 14:50 ?        00:00:42 /usr/bin/python2 /usr/bin/ansible-playbook --ssh-common-args=-F /var/lib/ovirt-engine/.ssh/config -v --private-key=/etc/pki/ovirt-engine/keys/engine_id_rsa --inventory=/tmp/ansible-inventory1162818200209914533 --extra-vars=target_directory="/save_ova/base/dump" --extra-vars=entity_type="vm" --extra-vars=ova_name="c8server.ova" --extra-vars=ovirt_ova_pack_ovf=" . . . ovf definition . . ." /usr/share/ovirt-engine/playbooks/ovirt-ova-export.yml

is only present for the first VM, so culd it be that the lock is perhaps at db level?
EG I see:  

engine=# select * from job order by start_time desc;
                job_id                |  action_type  |                                    descripti
on                                    | status  |               owner_id               | visible |  
       start_time         |          end_time          |      last_update_time      |            cor
relation_id            | is_external | is_auto_cleared | engine_session_seq_id 
--------------------------------------+---------------+---------------------------------------------
--------------------------------------+---------+--------------------------------------+---------+--
--------------------------+----------------------------+----------------------------+---------------
-----------------------+-------------+-----------------+-----------------------
 1f304799-5f86-422d-af60-46fd52047858 | ExportVmToOva | Exporting VM c8client as an OVA to /save_ova
/base/dump/c8client.ova on Host ov301 | STARTED | d1429f1f-2bea-4f60-bd2e-5bed997716ed | t       | 2
020-10-02 14:51:37.423+02 |                            | 2020-10-02 14:51:45.031+02 | e4276504-c2ca-
4454-996e-86a61cc265db | f           | t               |                  1247
 ea76fe36-7274-4603-870e-3f142e6e268b | ExportVmToOva | Exporting VM c8server as an OVA to /save_ova
/base/dump/c8server.ova on Host ov301 | STARTED | d1429f1f-2bea-4f60-bd2e-5bed997716ed | t       | 2
020-10-02 14:50:19.911+02 |                            | 2020-10-02 14:50:43.191+02 | 333df0a9-ccfe-
4034-9f67-e1cec49a4468 | f