Only override buildKey when overrideLatestBuild.

[marklagendijk]

This pull request makes sure that the buildKey of BitbucketBuildStatusNotifierStep calls, are not incorrectly overriden.

Current behaviour

1. Create a pipeline which calls bitbucketStatusNotify with a static buildKey, e.g. build.
2. Fail the pipeline, so Bitbucket gets a failed build.
3. Rerun the pipeline. Bitbucket will show it as a new build, instead of overriding the previous build result.

Fixed behaviour

1. Create a pipeline which calls bitbucketStatusNotify with a static buildKey, e.g. build.
2. Fail the pipeline, so Bitbucket gets a failed build.
3. Rerun the pipeline. Bitbucket will correctly replace the previous result, with the latest one.

[marklagendijk]

This fixes jenkins-40998 in an alternative way to #35.
I think this fix is better because it stays closer to the actual Bitbucket API.

[monkeybeans]

hi, will this be merged anytime soon? :)

[biodrone]

This fixes an issue I'm currently having, any chance of a review/merge soon?

[joaori]

I've also bumped into this issue when using a static buildKey with BitbucketBuildStatusNotifierStep.

Whenever a build is aborted and we attempt to run it again we have duplicate build status being created in Bitbucket (instead of being overridden). Which is a bit annoying when merge checks are in place...

@amansilla any chance this PR could be approved?
Thanks!

[Noraldeno]

Hello. Any plans for this PR be approved and merged soon? :D

[Noraldeno]

As a workaround until this PR is merged in, I instead just use curl to send build statuses to Bitbucket.

https://gist.github.com/Noraldeno/af0e339a48425db72dda118b0481e688