Keystoneclient create user API should have optional password.

Password is optional in Keystone service. The create user API
in keystoneclient should have password None as default value.

Change-Id: Ic72867c9b86ca65e3237786e35bcb5bd44f5f053
Closes-Bug: #1273988
Merge "Keystoneclient create user API should have optional password."
Test commit