Support for custom admin domain

[careys7]

Preconditions

1. Magento 2.2.2, MFTF

Steps to reproduce

1. Try to configure a custom admin domain (for example, admin.example.org)

Expected result

1. Configuration is available

Actual result

1. No applicable configuration appears to be documented

[careys7]

Closing this issue, it seems that the redirect is followed without any problems