Create user returns 400 without a password

If it is intended to create a new user without password (is optional)
keystone user-create --name <name>
keystone fails returning error 400.

The change consist in checking if the request has password: None
don't make the password hash

Co-Authored-By: huangtianhua<huangtianhua@huawei.com>
Closes-Bug: #1245342
Change-Id: If6f5789dcec0610a237f286d0d17ad4b100ef5f3
Merge "Create user returns 400 without a password"