Fix parsing begin time flag

[FluffyEscargot]

Closes #267

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

[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.