Zonebie should be able to iterate over every time zone

I am hesitant to use randomness in my tests, because sometimes a test would pass and then the next time I run it it would fail. If the test is truly failing because of time zone differences, that randomness would make it really hard to debug!

How about we add a way to iterate over every time zone? Something like this:

Zonebie.each_time_zone do |time_zone|
  #iterates through each ActiveSupport::TimeZone
  assert Something_in_the_db_is_always_in_UTC?
end

[bcherny]

that seems like a much better approach!