[SD-668]: Fixed:

Upsert of User Profile after successful Authentication into Mongo, was failing when AD is enabled.
Command users:copyfromad fails to insert user into Mongo.
Added AD check in UsersService to avoid adding hashed password to doc when AD is enabled
To be on the same page, does that mean having a service for each AUTH_MODE like `DBUserService` and `ADUserService`, and have the check `if 'LDAP_SERVER' in os.environ` in `users.init_app()` something like below:

```
    endpoint_name = 'users'
    service = ADUsersService(endpoint_name, backend=superdesk.get_backend()) if 'LDAP_SERVER' in os.environ else DBUsersService(endpoint_name, backend=superdesk.get_backend())
    UsersResource(endpoint_name, app=app, service=service)
```