schema: tracecback when using schema --annotate on single line dicts

[Chad Smith]

Annotate doesn't handle r-value dicts that begin on the same line as the l-value key.

Given the following example invalid cloudconfig (providing an int for a string value in chef), we get a traceback when trying to annotate the invalid user-data.

cat > invalid-chef-traceback.yaml <<EOF
#cloud-config
chef: {install_type: 1}
EOF

Annotate works on dicts that are not declared on the same line as the "chef" key

cat > invalid-chef.yaml <<EOF
#cloud-config
chef:
  install_type: 1
EOF

csmith@uptown:~/src/cloud-init$ python3 -m cloudinit.cmd.main devel schema -c invalid-chef.yaml --annotate
#cloud-config
chef:
   install_type: 1 # E1

# Errors: -------------
# E1: 1 is not of type 'string'

csmith@uptown:~/src/cloud-init$ python3 -m cloudinit.cmd.main devel schema -c invalid-chef-traceback.yaml --annotate
Traceback (most recent call last):
  File "/home/csmith/src/cloud-init/cloudinit/config/schema.py", line 215, in validate_cloudconfig_file
    validate_cloudconfig_schema(
  File "/home/csmith/src/cloud-init/cloudinit/config/schema.py", line 120, in validate_cloudconfig_schema
    raise SchemaValidationError(errors)
cloudinit.config.schema.SchemaValidationError: Cloud config schema errors: chef.install_type: 1 is not of type 'string'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.8/runpy.py", line 193, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.8/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "/home/csmith/src/cloud-init/cloudinit/cmd/main.py", line 901, in <module>
    return_value = main(sys.argv)
  File "/home/csmith/src/cloud-init/cloudinit/cmd/main.py", line 891, in main
    retval = util.log_time(
  File "/home/csmith/src/cloud-init/cloudinit/util.py", line 2285, in log_time
    ret = func(*args, **kwargs)
  File "/home/csmith/src/cloud-init/cloudinit/config/schema.py", line 444, in handle_schema_args
    validate_cloudconfig_file(
  File "/home/csmith/src/cloud-init/cloudinit/config/schema.py", line 219, in validate_cloudconfig_file
    print(annotated_cloudconfig_file(
  File "/home/csmith/src/cloud-init/cloudinit/config/schema.py", line 151, in annotated_cloudconfig_file
    errors_by_line[schemapaths[path]].append(msg)
KeyError: 'chef.install_type'

[Alberto Contreras (aciba)]

Another example:

```yaml
#cloud-config
users:
  - name: james
    hashed-passwd: somepassword
```

from https://github.com/canonical/cloud-init/pull/1549#pullrequestreview-1028680743

[Chad Smith (chad.smith)]

Let's address this, as there are a couple of failure paths in --annotate that really should be cleaned up for usability.

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/3754