MAAS cannot mark "broken" VMs as fixed without recommissioning

[Bill Wear]

On MAAS 3.2.6 (at least), VMs marked as "Broken" cannot be marked as "Fixed". This is because of the following code in `src/maasserver/node_action.py:785`:

```python
            script_failures = script_set.scriptresult_set.exclude(
                status=SCRIPT_STATUS.PASSED
            )
```

Since VMs skip `30-maas-01-bmc-config` -- because they don't actually authenticate thru a BMC -- it's impossible with the above code in place to ever come back from "Broken" without recommissioning the VM.

Note that https://code.launchpad.net/~igor-brovtsin/maas/+git/maas/+merge/431630 addresses this particular situation, but it's uncertain if there are other cases where a SKIP might not warrant a commissioning failure status, so filing the bug anyway.

[Bill Wear (billwear)]

for example, src/metadataserver/models/scriptresult.py:164 is another case where adding SKIPPED might be necessary.