Allow MAX_SECOND_LATE to be user defined

On certain hosts I don't have the option to run cf-agent at 5 minute intervals so this will allow you to specify the number of seconds to allow before throwing an alert.

Also, the get_last_line_of_file function had references two references to CF_PROMISE_SUMMARY_FILE which can be replaced with filepath
I don't dig the fact that `args` is coming from outside this function, while not being a global `CONSTANT`.
Isn't there a more elegant to pass it around in here?