A follow-up of https://bugzilla.redhat.com/show_bug.cgi?id=2353002

To allow reinstallations with home reuse on MBR-partitioned disks we relaxed the mount point constraints in https://github.com/rhinstaller/anaconda/pull/6306 to the point they are almost never applied (although thanks to backend checks invalid mount point assignment is not accepted). This is reflected in the test update it required: https://github.com/rhinstaller/anaconda-webui/pull/732/commits/156a6a1682056edf0729383af275ffdea0dce2ff

There is a WIP to fix the constraints by

• fixing backend API: https://github.com/rhinstaller/anaconda/pull/6312
• using it appropriately in the frontend: https://github.com/rhinstaller/anaconda-webui/pull/740

Goal:

Make the boot partiotion mount point constraints work correctly again.

Acceptance Criteria:

• Revert the https://github.com/rhinstaller/anaconda-webui/pull/732/commits/156a6a1682056edf0729383af275ffdea0dce2ff
• Create and pass a new test for the constraints that would use 2 preexisting disks (MBR-partitioned and GPT-partitioned) and check the correct application of the constraints and checks to home reuse enablement based on the disk selection.