It was assumed that the user would specify the reboot strategy as an
unquoted value. In the case that they turn off updates, `off` is
interpreted as a boolean and the normalization pass converts that to
`false`. In the event that the user uses `"off"`, it's interpreted as a
string and not modified.
In all of the YAML tags, - has been replaced with _. normalizeConfig() and
normalizeKeys() have also been added to perform the normalization of the input
cloud-config.
As part of the normalization process, falsey values are converted to "false".
The "off" update strategy is no exception and as a result the "off" update
strategy has been changed to "false".
