Add ability to prompt for passwords for user create and set

* Add get_password method to the utilities
* Add --password-prompt option
* Call the get_password method if a prompt is requested
* Various tests

Change-Id: I1786ad531e2a2fbcc21b8bc86aac0ccd7985995a
Closes-Bug: 1100116
Merge "Add ability to prompt for passwords for user create and set"