Whisk tests

[dapplion]

No description provided.

[hwwhww]

For ethereum#3424 update:

we noted that CURDLEPROOFS_N_BLINDERS + WHISK_VALIDATORS_PER_SHUFFLE must be a power of two

We can add an assertion in a new tests/core/pyspec/eth2spec/test/whisk/unittests/test_config_invariants.py file to verify it.

@with_whisk_and_later
@spec_test
@single_phase
def test_curdleproof(spec):
    assert spec.is_power_of_two(spec.CURDLEPROOFS_N_BLINDERS + spec.WHISK_VALIDATORS_PER_SHUFFLE)

I am noting this here because this PR introduces with_whisk_and_later decorator.

[dapplion]

Superseeded by ethereum#3442 but leaving open in case I need to do more tests

[Dawidowak]

Masakra