User Data registration via UI doesn't honour the domain field

##### ISSUE TYPE

* Bug Report

##### COMPONENT NAME

~~~
User Data
~~~

##### CLOUDSTACK VERSION

4.19 (would be present from 4.18 - when managed user data service support was added)
~~~

~~~

##### CONFIGURATION

##### OS / ENVIRONMENT

##### SUMMARY

Registration of user data in a specific domain i.e., by passing the domain in the UI , doesn't honour the domain id passed, rather creates the user data in the domain you are currently logged in to.

##### STEPS TO REPRODUCE

~~~
1. Log in as Admin
2. Create a domain - domain1 under ROOT domain
3. As Admin in the ROOT domain context, register a user data and pass domain as /domain1
4. User data is registered but the domain appears as ROOT and not /domain1
~~~

##### EXPECTED RESULTS

~~~
User data be registered in the correct domain
~~~

##### ACTUAL RESULTS

~~~
User data created / registered in the domain in the current context
~~~

Start by reproducing the User Data registration flow in the UI: create domain1 under ROOT, then register user data from the ROOT context while passing /domain1. Trace the UI registration entry point and the handling of the domain field. Done means the user data is created in domain1 rather than the current ROOT domain.

Written by the indexing model from the issue text.