Disabling validation plugin doesn't wait for tempest charm to be fully removed

[Tianqi Xiao]

Currently when disabling validation plugin, the process is marked as completed before tempest is fully removed. As shown in the code snippet below, the tempest charm is still in the middle of clean-up process at the time validation plugin is considered successfully disabled. From my tests, the model will eventually settle and tempest charm will be gone, but if for some reason an issue comes up, we will not be able to catch the error.

```
ubuntu@sunbeam02:~$ sunbeam disable validation
OpenStack validation application disabled.
ubuntu@sunbeam02:~$ juju status -m openstack
Model Controller Cloud/Region Version SLA Timestamp
openstack sunbeam-controller sunbeam-microk8s/localhost 3.4.0 unsupported 15:09:53Z

SAAS Status Store URL
microceph active local admin/controller.microceph

App Version Status Scale Charm Channel Rev Address Exposed Message
certificate-authority active 1 self-signed-certificates latest/beta 109 10.152.183.56 no
cinder active 1 cinder-k8s 2023.2/edge 63 10.152.183.50 no
cinder-ceph active 1 cinder-ceph-k8s 2023.2/edge 57 10.152.183.151 no
cinder-ceph-mysql-router 8.0.34-0ubuntu0.22.04.1 active 1 mysql-router-k8s 8.0/candidate 82 10.152.183.101 no
cinder-mysql-router 8.0.34-0ubuntu0.22.04.1 active 1 mysql-router-k8s 8.0/candidate 82 10.152.183.38 no
glance active 1 glance-k8s 2023.2/edge 77 10.152.183.145 no
glance-mysql-router 8.0.34-0ubuntu0.22.04.1 active 1 mysql-router-k8s 8.0/candidate 82 10.152.183.133 no
horizon active 1 horizon-k8s 2023.2/edge 75 10.152.183.186 no http://10.6.0.182/openstack-horizon
horizon-mysql-router 8.0.34-0ubuntu0.22.04.1 active 1 mysql-router-k8s 8.0/candidate 82 10.152.183.80 no
keystone active 1 keystone-k8s 2023.2/edge 168 10.152.183.169 no
keystone-mysql-router 8.0.34-0ubuntu0.22.04.1 active 1 mysql-router-k8s 8.0/candidate 82 10.152.183.182 no
mysql 8.0.34-0ubuntu0.22.04.1 active 1 mysql-k8s 8.0/candidate 113 10.152.183.94 no
neutron active 1 neutron-k8s 2023.2/edge 70 10.152.183.121 no
neutron-mysql-router 8.0.34-0ubuntu0.22.04.1 active 1 mysql-router-k8s 8.0/candidate 82 10.152.183.213 no
nova active 1 nova-k8s 2023.2/edge 66 10.152.183.106 no
nova-api-mysql-router 8.0.34-0ubuntu0.22.04.1 active 1 mysql-router-k8s 8.0/candidate 82 10.152.183.24 no
nova-cell-mysql-router 8.0.34-0ubuntu0.22.04.1 active 1 mysql-router-k8s 8.0/candidate 82 10.152.183.187 no
nova-mysql-router 8.0.34-0ubuntu0.22.04.1 active 1 mysql-router-k8s 8.0/candidate 82 10.152.183.49 no
ovn-central active 1 ovn-central-k8s 23.09/edge 75 10.152.183.246 no
ovn-relay active 1 ovn-relay-k8s 23.09/edge 62 10.6.0.181 no
placement active 1 placement-k8s 2023.2/edge 58 10.152.183.242 no
placement-mysql-router 8.0.34-0ubuntu0.22.04.1 active 1 mysql-router-k8s 8.0/candidate 82 10.152.183.243 no
rabbitmq 3.12.1 active 1 rabbitmq-k8s 3.12/edge 33 10.6.0.183 no
tempest blocked 1/0 tempest-k8s 2023.2/edge 21 10.152.183.202 no (identity-ops) integration missing
traefik 2.10.4 active 1 traefik-k8s 1.0/edge 164 10.6.0.184 no
traefik-public 2.10.4 active 1 traefik-k8s 1.0/edge 164 10.6.0.182 no

Unit Workload Agent Address Ports Message
certificate-authority/0* active idle 10.1.56.199
cinder-ceph-mysql-router/0* active idle 10.1.56.206
cinder-ceph/0* active idle 10.1.56.208
cinder-mysql-router/0* active idle 10.1.56.223
cinder/0* active idle 10.1.56.230
glance-mysql-router/0* active idle 10.1.56.219
glance/0* active idle 10.1.56.228
horizon-mysql-router/0* active idle 10.1.56.202
horizon/0* active idle 10.1.56.217
keystone-mysql-router/0* active idle 10.1.56.225
keystone/0* active idle 10.1.56.229
mysql/0* active idle 10.1.56.204 Primary
neutron-mysql-router/0* active idle 10.1.56.215
neutron/0* active idle 10.1.56.201
nova-api-mysql-router/0* active idle 10.1.56.212
nova-cell-mysql-router/0* active idle 10.1.56.209
nova-mysql-router/0* active idle 10.1.56.203
nova/0* active idle 10.1.56.231
ovn-central/0* active idle 10.1.56.214
ovn-relay/0* active idle 10.1.56.205
placement-mysql-router/0* active idle 10.1.56.222
placement/0* active idle 10.1.56.220
rabbitmq/0* active idle 10.1.56.224
tempest/0* blocked executing 10.1.56.232 (identity-ops) integration missing
traefik-public/0* active idle 10.1.56.210
traefik/0* active idle 10.1.56.216

Offer Application Charm Rev Connected Endpoint Interface Role
cert-distributor keystone keystone-k8s 168 1/1 send-ca-cert certificate_transfer provider
certificate-authority certificate-authority self-signed-certificates 109 1/1 certificates tls-certificates provider
cinder-ceph cinder-ceph cinder-ceph-k8s 57 1/1 ceph-access cinder-ceph-key provider
keystone keystone keystone-k8s 168 1/1 identity-credentials keystone-credentials provider
ovn-relay ovn-relay ovn-relay-k8s 62 1/1 ovsdb-cms-relay ovsdb-cms provider
rabbitmq rabbitmq rabbitmq-k8s 33 1/1 amqp rabbitmq provider
```