Invalid write_files format doesn't make the cloud-init fail

[manuel]

If the cloud config file format is not correct (see example below), the write_files module fails, but the cloud-init status is done

Cloud-config file:

```
#cloud-config

write_files:
  - content: |
      line below is badly indented
ouch!

    path: /tmp/cloud-init-file.txt
```

Extract of cloud-init-output.log
```
2020-03-18 13:54:05,321 - util.py[WARNING]: Failed loading yaml blob. Invalid format at line 6 column 1: "while scanning a simple key
  in "<unicode string>", line 6, column 1:
    ouch!
    ^
could not found expected ':'
  in "<unicode string>", line 8, column 9:
        path: /tmp/cloud-init-file.txt
            ^"
2020-03-18 13:54:05,337 - util.py[WARNING]: Failed loading yaml blob. Invalid format at line 6 column 1: "while scanning a simple key
  in "<unicode string>", line 6, column 1:
    ouch!
    ^
could not found expected ':'
  in "<unicode string>", line 8, column 9:
        path: /tmp/cloud-init-file.txt
            ^"
2020-03-18 13:54:05,337 - util.py[WARNING]: Failed at merging in cloud config part from part-001
```

cloud-init status:
```
status: done
```

[Scott Moser (smoser)]

reproduces with:

$ cat ud.yaml
#cloud-config
runcmd:
- "echo hi world | tee /run/runcmd.log"
 - "echo this is indented one space more, making bad yaml"

$ ud=$(cat ud.yaml)
$ lxc launch ubuntu-daily:bionic btest --config=user.user-data="$ud"

$ lxc exec btest -- cloud-init status --wait ; echo $?
status: done
0

$ lxc exec btest /bin/bash
root@btest:~# grep WARN /var/log/cloud-init.log
2020-03-18 15:31:29,490 - util.py[WARNING]: Failed loading yaml blob. Invalid format at line 2 column 1: "while parsing a block mapping
2020-03-18 15:31:29,499 - util.py[WARNING]: Failed loading yaml blob. Invalid format at line 2 column 1: "while parsing a block mapping
2020-03-18 15:31:29,499 - util.py[WARNING]: Failed at merging in cloud config part from part-001
root@btest:~# grep errors /run/cloud-init/result.json
  "errors": []
root@btest:~# grep errors /run/cloud-init/status.json
   "errors": [],
   "errors": [],
   "errors": [],
   "errors": [],
   "errors": [],

[Scott Moser (smoser)]

Just verified this is still present (focal)
# cloud-init --version
/usr/bin/cloud-init 20.2-45-g5f7825e2-0ubuntu1~20.04.1

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/3627