Add reason field to function to hold function creation errors

[rjew]

Fixes #483

• Add reason field to function object
• When an error occurs during the function image build phase, return the last step that occurred (the one that failed) along with its output as the reason
  • It's difficult to determine the exact cause of the error since Docker combines both stdout and stderr into one stream
  • The only error Docker gives is the last command that failed

[tenczar]

Does this change populate the reason field when an error happens? It doesn't look like it would to me.

[rjew]

It does update the reason field. There was already a deferred call to h.Store.UpdateWithError in the function-manager controller.

[imikushin]

An e2e-test of a failing function creation (e.g. with an invalid handler) would clearly demonstrate the reason field being populated

[rjew]

Good point. I'll add an e2e test.

[imikushin]

Looks great!

[tenczar]

cool