Convert csk rollover test cases to pytest

Convert csk rollover test cases to pytest

Move the 'csk-roll1' and 'csk-roll2' zones to the rollover test dir and
convert CSK rollover tests to pytest.

The DS swap spans multiple steps. Only the first time we should check
if the "CDS is now published" log is there, and only the first time we
should run 'rndc dnssec -checkds' on the keys. Add a new key to the
step dictionary to disable the DS swap checks.

This made me realize that we need to check for "is not None" in case
the value in the dictionary is False. Update check_rollover_step()
accordingly, and also add a log message which step/zone we are currently
checking.