From this helper's docstring:

    Ubuntu cloud images previously included a 'eth0.cfg' that had
    hard coded content.  That file would interfere with the rendered
    configuration if it was present.

This code is no longer relevant due to the following:

1) Ubuntu uses netplan
2) This appears like an Ubuntu-specific workaround
3) Debian cloud images use netplan

Remove unnecessary arguments.

Since Python 3.6, json.loads() is capable of receiving arguments of type
str, bytes, and bytearray. Cloud-init's code historically manually handled type
conversion. This boilerplate is no longer necessary.

Add docstring and typing to util.load_json().

Cloud-init's codebase makes extensive use of exception handlers which
catch Exception and then do something based on the assumed exception
type. This is bad practice and makes it possible for exceptions to be
unexpectedly ignored. To remedy this, this commit updates cloud-init to
make `Exception` always be an unknown exception which therefore should
always produce a log of level `WARN` or higher.

Require a minimum of one of the following in each Exception handler:

- LOG.warning("Unhandled exception: %s", e)
- util.logexc() - with a log level of WARN or higher
- re-raise the exception without setting exception type when
  re-raising[1]

Make cloud-init's code adhere to the above set of rules with the
following changes:

- Limit the scope where Exception is handled to only unexpected error paths.
- Add new handlers for more specific exception types.
- Add warning logs or increase log level to WARN in some cases.
- Add typing where exceptions are returned.
- Replace various Exception handlers with ProcessExecutionError.
- Remove handling that does nothing.
- Remove unused code which handles Exception.

[1] This would likely reduce the scope of the exception and make it
    possible to mask an Exception.

In Python 3.3+, IOError is an alias of OSError[1]. Some call sites use
one or the other or both. Standardize on the OSError.

[1] https://docs.python.org/3/library/exceptions.html#IOError