Return codes.InvalidArgument to rather return HTTP 400 instead of HTTP 500

[vaporz]

1, Same change in "template.go" with #397 .
2, Add a test case.
3, Update examples

[vaporz]

Ah...."Waiting for status to be reported", why....

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[vaporz]

I signed it!

[vaporz]

zzzZZZ

[googlebot]

CLAs look good, thanks!

[vaporz]

ping @tamalsaha , @tmc
Thank you.

[pieterlouw]

I will close #397 as this PR have test case and examples

[vaporz]

Hi, any comments on this PR?
Thanks!

[tmc]

lgtm, @achew22 @tamalsaha one of you want to weigh in?

[tamalsaha]

LGTM.