[core_ibex,dv] Name RTL runs by seed, not iteration index
[core_ibex,dv] Name RTL runs by seed, not iteration index

This makes path calculations a bit easier when it comes to loading
stuff up for comparison (allowing us to move more into the Makefile).
Long-term, it might also allow us to change how we track things
entirely, getting rid of the start-seed part of the output directory
structure.

lowRISC/ibex,lowRISC/ibex,AmbiML/ibex,AmbiML/ibex,AmbiML/ibex,AmbiML/ibex,lowRISC/ibex,lowRISC/ibex