Return error on non-200 responses

[vicmarbev]

Handle http errors as specified in #682. The resolution is the same as in carvel-dev/kapp#523

[vicmarbev]

The linter fails with:
pkg/files/sources.go:91:1: exported: exported function NewHTTPSource should have comment or be unexported (revive) func NewHTTPSource(path string) HTTPSource { return HTTPSource{path, &http.Client{}} }
but this function already existed. Should I add a comment?

[cppforlife]

Should I add a comment?

yeah, linter is a bit too strict.

[gcheadle-vmware]

I've read through the referenced issue in kapp, and can confirm that these changes are identical to the change made in the kapp repo. Everything looks good to me 👍

[praveenrewar]

LGTM!

[pivotaljohn]

Thanks, @vicmarbev!

[pivotaljohn]

Published in v0.42.0.