Verified on iso 417-mos:
deletion of deploy tasks leads deletion of its child tasks
[root@nailgun ~]# fuel2 task list
+----+---------+-------------------------+---------+--------+----------+
| id | status  | name                    | cluster | result | progress |
+----+---------+-------------------------+---------+--------+----------+
|  1 | ready   | dump                    | None    | {}     |      100 |
|  7 | ready   | dump                    | None    | {}     |      100 |
|  8 | error   | deploy                  | 1       | {}     |      100 |
| 10 | error   | check_before_deployment | 1       | {}     |      100 |
| 11 | error   | deploy                  | 1       | {}     |      100 |
| 14 | ready   | node_deletion           | 1       | {}     |      100 |
| 16 | error   | deployment              | 1       | {}     |      100 |
| 17 | running | deploy                  | 2       | {}     |        7 |
| 20 | running | provision               | 2       | {}     |       23 |
| 21 | running | deployment              | 2       | {}     |        0 |
+----+---------+-------------------------+---------+--------+----------+
[root@nailgun ~]# fuel task --delete --tid 8
Tasks with id's 8 deleted.
[root@nailgun ~]# fuel2 task list
+----+---------+---------------+---------+--------+----------+
| id | status  | name          | cluster | result | progress |
+----+---------+---------------+---------+--------+----------+
|  1 | ready   | dump          | None    | {}     |      100 |
|  7 | ready   | dump          | None    | {}     |      100 |
| 11 | error   | deploy        | 1       | {}     |      100 |
| 14 | ready   | node_deletion | 1       | {}     |      100 |
| 16 | error   | deployment    | 1       | {}     |      100 |
| 17 | running | deploy        | 2       | {}     |       28 |
| 20 | running | provision     | 2       | {}     |       99 |
| 21 | running | deployment    | 2       | {}     |        0 |
+----+---------+---------------+---------+--------+----------+
[root@nailgun ~]# fuel task --delete --tid 11
Tasks with id's 11 deleted.
[root@nailgun ~]# fuel2 task list
+----+---------+------------+---------+--------+----------+
| id | status  | name       | cluster | result | progress |
+----+---------+------------+---------+--------+----------+
|  1 | ready   | dump       | None    | {}     |      100 |
|  7 | ready   | dump       | None    | {}     |      100 |
| 17 | running | deploy     | 2       | {}     |       28 |
| 20 | running | provision  | 2       | {}     |       99 |
| 21 | running | deployment | 2       | {}     |        0 |
+----+---------+------------+---------+--------+----------+



cat /etc/fuel_build_id:
 417
cat /etc/fuel_build_number:
 417
cat /etc/fuel_release:
 9.0
cat /etc/fuel_openstack_version:
 mitaka-9.0
rpm -qa | egrep 'fuel|astute|network-checker|nailgun|packetary|shotgun':
 fuel-release-9.0.0-1.mos6347.noarch
 fuel-bootstrap-cli-9.0.0-1.mos284.noarch
 fuel-migrate-9.0.0-1.mos8398.noarch
 fuel-mirror-9.0.0-1.mos137.noarch
 fuel-notify-9.0.0-1.mos8398.noarch
 nailgun-mcagents-9.0.0-1.mos746.noarch
 python-fuelclient-9.0.0-1.mos316.noarch
 fuelmenu-9.0.0-1.mos270.noarch
 fuel-9.0.0-1.mos6347.noarch
 fuel-utils-9.0.0-1.mos8398.noarch
 fuel-setup-9.0.0-1.mos6347.noarch
 fuel-library9.0-9.0.0-1.mos8398.noarch
 shotgun-9.0.0-1.mos90.noarch
 fuel-agent-9.0.0-1.mos284.noarch
 fuel-ui-9.0.0-1.mos2706.noarch
 fuel-ostf-9.0.0-1.mos934.noarch
 fuel-misc-9.0.0-1.mos8398.noarch
 python-packetary-9.0.0-1.mos137.noarch
 fuel-nailgun-9.0.0-1.mos8709.noarch
 rubygem-astute-9.0.0-1.mos746.noarch
 fuel-provisioning-scripts-9.0.0-1.mos8709.noarch
 network-checker-9.0.0-1.mos72.x86_64
 fuel-openstack-metadata-9.0.0-1.mos8709.noarch