Fix password field name

Fix password field name according to OpenStack documentation
http://api.openstack.org/api-ref-identity.html#identity-v2.
Example of json request
{
  "user": {
    "username": "jqsmith",
    "email": "john.smith@example.org",
    "enabled": true,
    "OS-KSADM:password": "secrete"
  }
}