Add configurable option for the user password length of the user
defined by the `username` config option. The following parameter
has been added:
- user_password_length: type=int, default=20
The current default password length is 20, making it cumbersome for
users to enter the lengthy password via console.
Change-Id: I37ae75a438f6fd326101c7b8a855c1f39dd1e804
Closes-bug: #1684119
894b800d31