misleading application status if charm does not set a status

[Samuel Allan]

If a charm doesn't set any status, the `juju status` output is somewhat misleading. It appears to be hanging at waiting for "installing agent". While actually here it's all up and running, just the charm hasn't set a status yet. For example:

```
Model Controller Cloud/Region Version SLA Timestamp
zaza-8bc91a62ca54 server-microk8s server-microk8s/localhost 2.9.32 unsupported 07:28:31+09:30

App Version Status Scale Charm Channel Rev Address Exposed Message
glance waiting 1 glance-k8s edge 3 10.152.183.227 no installing agent
keystone waiting 1 keystone-k8s 0 10.152.183.110 no installing agent
mysql active 1 sunbeam-mysql-k8s beta 4 10.152.183.101 no

Unit Workload Agent Address Ports Message
glance/0* unknown idle 10.1.206.224
keystone/0* unknown idle 10.1.206.194
mysql/0* active idle 10.1.206.216
```

It would be nice if juju cleared the application status, or updated it to some message to indicate that everything was successful with the agent and now it's handed status control over to the charm.

[Juan M. Tirado (tiradojm)]

The message displayed in the `juju status` is a section reserved for charms. This means that if Juju sets the value of this field, it may disrupt the charm lifecycle with erroneous messages. This is more a charm design issue rather than a Juju problem. Said that, we will consider this comment for further improvement. Thanks for taking your time to report this.

[John A Meinel (jameinel)]

This is worth investigating, because Juju does set the application status up until the point where the agent is installed, and then sets it to unknown once install has had a chance to run (if it didn't otherwise set its status), which is what you see from the unit status.

We probably need to tweak our application status to be set to unknown at the correct time.

[Ian Booth (wallyworld)]

The next 2.9.46 candidate release will not include a fix for this bug and we don't plan on any more 2.9 releases. As such it is being removed from its 2.9 milestone.

If the bug is still important to you, let us know and we can consider it for inclusion on a 3.x milestone.