Run only on even slots for R3, R4, R5

Powerboards are only installed in even carrier-board slots for R4 and R5.

For R3, which has two AMACs, both slots are in use, but should not be used independently.

This MR enforces the user to use an even slot, if testing and R3/R4/R5 PB.

Depends on !158 (merged)

Tagging @kkrizka