better handling of subordinate departed states

[kwmonroe]

Lots of things don't work when control plane subordinates depart. kubectl get $stuff is especially troublesome as it takes forever to timeout. When we know our subs are going away, don't run things that call kubectl get $stuff like get_dns_ip and configure_cdk_addons.

Fixes https://bugs.launchpad.net/charm-kubernetes-master/+bug/1968237

[kwmonroe]

Looks good:

$ time juju destroy-model diehard -y
Destroying model
Waiting for model to be removed, 10 machine(s), 7 application(s)................
......
Waiting for model to be removed, 9 machine(s), 7 application(s)....
Waiting for model to be removed, 8 machine(s), 7 application(s)......
Waiting for model to be removed, 7 machine(s), 7 application(s)...
Waiting for model to be removed, 6 machine(s), 7 application(s)........
Waiting for model to be removed, 5 machine(s), 7 application(s).................
..
Waiting for model to be removed, 4 machine(s), 7 application(s)...
Waiting for model to be removed, 3 machine(s), 7 application(s)...
Waiting for model to be removed, 2 machine(s), 7 application(s).................
...............................
Waiting for model to be removed, 2 machine(s), 6 application(s)...............
Waiting for model to be removed, 2 machine(s), 5 application(s).............
Waiting for model to be removed, 2 machine(s), 4 application(s).................
.
Waiting for model to be removed, 2 machine(s), 3 application(s).............
Waiting for model to be removed, 2 machine(s), 2 application(s).........
Waiting for model to be removed, 1 machine(s), 2 application(s).................
.....
Waiting for model to be removed, 1 machine(s), 1 application(s).................
.......
Waiting for model to be removed, 1 machine(s)....
Model destroyed.

real	6m57.537s
user	0m0.240s
sys	0m0.295s

7 minutes is considerably better than the ♾️ minutes it was taking before.

[kwmonroe]

/hold to flesh this out in charmed-kubernetes/layer-kubernetes-common#28

[addyess]

Yep, this look pretty nice.

[addyess]

Random nit: this method could REALLY use some return typing

def get_dns_info() -> Tuple[bool, Optional[str], Optional[int], Optional[str]]:

Suggested change

	if dns_ip:
	return True, dns_ip, 53, dns_domain
	else:
	return False, None, None, None
	if dns_ip:
	return True, dns_ip, 53, dns_domain
	return False, None, None, None

[addyess]

@kwmonroe i'm still good with this one