This adds an Exception that extends the Python stdlib
subprocess.CalledProcessError.

The difference is that the str() method of this exception also adds the
stdout/stderr logs. In effect, if this exception goes unhandled, Python
will print the output in a visually distinct wrapper to the terminal so
that it's easy to spot in a sea of traceback information.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220321201618.903471-3-jsnow@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>