check_if_image_tag_exists fails if multiple tags are created on the same hash

[katsew]

Hi, I use gcr.io/gcp-runtimes/check_if_tag_exists:latest to check existing tags.
However the image_tag will be like foo,bar when multiple tags are created on the same hash,
the build function cannot recognize the tag and the step passed through the check.

I think split tag string with comma, then flatten existing_tags before create a set to fix this problem.

def check_if_tag_exists(raw_image_path, force_build):
        ...
        existing_tags = []
        for tag in output.split('\n'):
            tag = tag.rstrip().split(',')
            existing_tags = sum([tag], existing_tags)
        existing_tags = set(existing_tags)
        ...

I will make a patch if it is ok to fix.

[nkubala]

@katsew thanks for the issue. our teams aren't actively maintaining this repository anymore, but feel free to submit fixes as you find them and we'll do our best to push out releases!