Fix parsing begin time flag

[FluffyEscargot]

Closes #267

• Parsing of start time failed, because regex produces 3 matching groups, not more

[deitch]

1. Can we split this into 2 changes? Based on the comment on the issue, the discussion around "how to fix date parsing which is broken" is distinct from the discussion around "how to support timezones".
2. Can we include a test for this? We already have TestWaitForCron() which was the most important part to get right, given its complexities), so this should be easy enough to add. More importantly, it will help explain the use cases here.

[FluffyEscargot]

I've added the tests to cover basic cases, not looking at timezones yet.
What I haven't included yet, is some inputs which pass, even though they shouldn't in my opinion:

{"fail invalid time", "2401", "2018-10-10T10:00:00Z", time.Duration(0), fmt.Errorf("invalid format for begin delay '2401'")},
{"fail too long time", "12345", "2018-10-10T10:00:00Z", time.Duration(0), fmt.Errorf("invalid format for begin delay '12345'")},

1. 2401, time.Date accepts values outside the usual range, so doesn't have to be <24 and <60 for hours and minutes
2. 12345, the regex currently allows for leading or trailing characters, so aaaa2309bbbb also passes. Adding ^ and $ to begin and end of the regex would fix that

[deitch]

I've added the tests to cover basic cases, not looking at timezones yet.

Thanks. Keeps it cleaner.

What I haven't included yet, is some inputs which pass, even though they shouldn't in my opinion:

So I should wait to kick off CI?

[FluffyEscargot]

Ready to merge

[deitch]

All looks good, but needs a rebase.