cron_test: fix bug in tests leading to flakiness
cron_test: fix bug in tests leading to flakiness

Test[Non]LocalTimezone was occasionally specifying an invalid cron spec seconds
field of "59,60", which caused it to subsequently fail. Since rolling the cron
spec forward is hard, in those cases we instead sleep for a couple seconds to
avoid the scenario.

Fixes #205

robfig/cron