juju happily deploys a machine bundle on a k8s model

[Leon]

I accidentally asked juju to deploy the following machine bundle on a k8s model:

series: jammy
saas:
  prom:
    url: k8s2:admin/cos.prom
applications:
  cos-proxy:
    charm: ./cos-proxy_ubuntu-20.04-amd64_ubuntu-22.04-amd64.charm
    series: focal
    num_units: 1
  nrpe:
    charm: nrpe
    channel: edge
    revision: 114
  ub:
    charm: ubuntu
    channel: stable
    revision: 24
    series: focal
    num_units: 1
relations:
- - cos-proxy:downstream-prometheus-scrape
  - prom:metrics-endpoint
- - nrpe:monitors
  - cos-proxy:monitors
- - nrpe:general-info
  - ub:juju-info

As a result, the deploy command errored out, but cos-proxy and nrpe were deployed nonetheless:

$ juju deploy ./lxd-bundle.yaml
Located charm "nrpe" in charm-hub, channel edge
Located charm "ubuntu" in charm-hub, channel stable
Executing changes:
- upload charm /home/ubuntu/code/o11y/cos-proxy-operator/cos-proxy_ubuntu-20.04-amd64_ubuntu-22.04-amd64.charm for series focal with architecture=amd64
- deploy application cos-proxy on focal
- upload charm nrpe from charm-hub for series jammy with revision 114 with architecture=amd64
- deploy application nrpe from charm-hub on jammy with edge
- upload charm ubuntu from charm-hub for series focal with revision 24 with architecture=amd64
- deploy application ub from charm-hub on focal with stable using ubuntu
ERROR cannot deploy bundle: cannot deploy application "ub": block storage "block" is not supported for container charms

---

I'd expect this deploy command to fail without any charms deployed, because:
1. The bundle didn't specify `bundle: kubernetes` but is attempted on a k8s model.
2. The charms are machine charms, but attempted on a k8s model.
3. The error "block storage "block" is not supported for container charms" could potentially be flagged before going forward with any charm deployments.

[Ian Booth (wallyworld)]

There's really no such thing as a "machine charm". If by machine charm you mean a charm which does not define any workload containers, then that's still a valid k8s charm; it's a "pure" operator charm for want of a better term.

We should fail early though if a bundle is not valid for the model.