Packit: Drop tests for obsoleted upgrade paths + restructuralisation

Dropping upgrade paths related to following releases: 8.6, 8.9, 9.0,
9.3. See the previous commit for more info.

During the drop of these release, I've realized the current structure
of tests is not suitable for such operations as current test/job
definitions has been chained. So e.g. tests for 8.10 -> 9.4 depended
on 8.9 -> 9.3, which depended on 8.8 -> 8.6, etc... Even going deeper,
IPU 8->9 definitions have been based on 7 -> 8 definitions.

So I updated the structure, separating tests for IPU 7 -> 8 and 8 -> 9
and also deps between all upgrade paths. Now, particular tests
can inherit one of *abstract* jobs definitions, so dropping or removing
tests for an upgrade path does not affect other tests.

Also fixed some incorrect definitions.

Author: pirat89