document the usage of userdata for cloud-init

closes #14643
Merge pull request #14713 from saltstack/bp-14700

Backport #14700 to 2014.7
Lint fixes
lint
lint
`__file__` is not set in an `exec()` context
Fixing the case when the cmd for a cron job is updated but the changes don't reflect the change.
Ensure that identifier and cmd arguments to _check_cron are strings, as both returned from list_tab will be strings.
Should not .lower the cmd
Don't lower identifier either.