Fix 'latest' tagging
Fix 'latest' tagging

Per [1], only a single image should have 'latest' in any of its tags,
so tags like 'latest-hadoop27' should just be 'hadoop27'.

For source variants like 'alpine', the variant name should replace
'latest'.

[1]https://github.com/docker-library/official-images/tree/101ca042533353c702893d0c39578077e2b872d4#tags-and-aliases

docker-flink/docker-flink