Avoid displaying password with help message
Avoid displaying password with help message

When setting password using the MARATHON_PASSWORD environment
variable, the password was plainly displayed along with the help
message ``marathon --help``.

This fix 'hides' the password to the help message.

criteo-forks/marathon-api,otto-de/marathon-api,otto-de/marathon-api,criteo-forks/marathon-api,davidcollom/marathon-api,davidcollom/marathon-api