Fix error detection case when image that is being deleted does not exist - continued.

[bendavies]

Summary

Corrects the fix provided in #1897.

We were experiencing images not being removed and upgraded ecs-agent to fix the issue, after seeing the above PR.
It did not fix the issue.

Investigation revealed that the above PR does not fix the issue (at least for more recent docker versions because the actual error return from docker is Error: No such image - capital N.

Implementation details

Make the string contains check for no such image case insensitive.

Testing

• update test TestDeleteImageNotFoundError to make the error the correct case.
• left test TestDeleteImageNotFoundOldDockerMessageError alone, using existing lower case error message. I am not sure if that is the correct case for old docker versions, but now we have 2 tests covering both cases.

New tests cover the changes: yes, corrected existing.

Description for the changelog

Bug - Fix cleaning up images when some images are not found. Continuation of #1897

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[bendavies]

By the way, can someone explain to me how the original report #1871 was fixed?
The original report was that processing of image removal stops abruptly when the first not found image was encountered, but I can't follow or see how that occurs at all. I'm not a Go person however, so that might explain it :)

[yhlee-aws]

Could you fix the error reported by travis and update this PR please?
agent\engine\docker_image_manager.go:541:23: cannot refer to unexported name strings.toLower
agent\engine\docker_image_manager.go:541:23: undefined: strings.toLower

Also, PR #1897 is the PR that's fixing issue #1871.

[bendavies]

hi @yunhee-l thanks - fixed.
Yes, I mention #1897 in my OP, but I can't see how it fixes the symptom of image removal being halted after encountering a not found image, as described in #1871. Maybe i'm missing something obvious.

[bendavies]

ping @shubham2892 as the original fixer

[shubham2892]

By the way, can someone explain to me how the original report #1871 was fixed?

@bendavies Thanks for looking into this.

As far as I remember, it's related to the cleaning that happens after the If statement, feel free to explore this case more, it's possible I might have missed something.

[shubham2892]

@bendavies Can you rebase the branch against dev please. Thanks.

[bendavies]

@shubham2892 done

[bendavies]

will this make it into V1.28.0?

[yhlee-aws]

It should be in V1.29.0.