Adds possibility to change another user password

[github at samba.org]

New comment by hortimech on Samba Github repository

https://github.com/samba-team/samba/pull/42#issuecomment-174476911
Comment:
Can somebody explain why the code in source4 needs to be altered when samba-tool already does what GuillaumeGomez is trying to do

i.e.
samba-tool user setpassword --help
Usage: samba-tool user setpassword (<username>|--filter <filter>) [options]

Set or reset the password of a user account.

The command may be run from the root userid or another authorized userid.  The
-H or --URL= option can be used to execute the command against a remote
server.

I am not adverse to changes if they are required and helpful, but are they needed here ?