[prosEO CLI] Option -u : enhancement of the 'help' documentation and user login in general about proseo

[tangobravo62]

Fixed: The comment has been changed to not suggest that a default user from the configuration file will be used in case of no login:

Options for the 'proseo' command:
    -v, --version     Show the prosEO CLI version and exit (only for call from shell command line)
    -u, --user        The user name for login to prosEO.
    -p, --password    The password for login to prosEO (only valid if a user name for login is given).
    -m, --mission     The mission to login to (only valid if a user name for login is given)

The code was corrected to actually honour the login parameters (was not the case so far).