nethvoice: test freepbx user domain change

[Amygos]

Test the behavior of a change of the users' domain after the first configure-module

[Stell0]

when user domain is changed

• new users are saved into userman_users table.
• rest_devices_phones table isn't changed
• rest_users isn't touched
• extensions aren't removed

there are three possible solutions, all requires some coding:

• Prevent the user domain change (requires work on the interface and documentation)
• Delete everything when changing (a warning on the interface would be appropriate)
• Delete everything and save the state to allow reverting to the old user provider (requires some coding and extensive testing)

[Stell0]

solution choosen is to show a warning on NS8 interface if user try to change an already configured user provider and delete all users and extensions from nethvoice