RFR: update-sync labels should be applied to all-bar-one records

[Kevin Rushforth]

On Fri, 25 Sep 2020 14:26:18 GMT, Rob McKenna <robm at openjdk.org> wrote:

> This modification fixes the situation where a backport record may be a member
> of two distinct streams and has its hgupdate-sync label removed as a result.
> 
> E.g. with backport records for 14, 15, 14.0.1, 15.0.1 no label would be
> applied to 15. The current logic gives precedence to the fact that it is the
> first release in the 15-updates stream and ignores the fact that it is not
> the first release in the feature stream. The label added by the feature stream
> is removed when evaluating the 15-updates stream. This should not be the case.

The fix looks good to me. One question about the test: is the `assertNotLabeled` method really needed? It looks like
`assertLabeled` will fail unless the set of issues with the labels is exactly as expected (i.e., it will fail if it
finds an issue that should have the sync label but doesn't or if if find an issue that should not have the sync label
but does), unless I'm missing something.

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Marked as reviewed by kcr (no project role).

PR: https://git.openjdk.java.net/skara/pull/848