Revisit Fork Choice tests

[anshalshukla]

Currently some of the forkchoice rules are written in a fashion that assumes that we get a new validator for each slot but in reality the default config with 4 validator is being used which is rotated in round robin fashion.
Todos:

• Revisit all the tests to see if it is works as intended even with the default 4 validator set.
• Eg: test_three_block_deep_reorg is incorrect, it doesn't follow the scenario described in the doc string. Total number of validators are 4 so fork A cannot have 3 blocks, and fork B with 4 blocks. some validator votes are being overwritten. Can be fixed by adding multiple validators at genesis, like done in test_reorg_with_slot_gaps
• I've just mentioned one case above but there might be more so it's good if we can revisit all of them to ensure everything is as intended.