Fix reporting status on first build when using multibranch pipelines

[jninnes]

Supercedes #46. I've taken that PR and built it with the latest Jenkins Bom for easier dependency management.

Fixes JENKINS-40456

Testing done

• Created a multibranch pipeline job.
• Created a new branch in repository for that job.
• Ensure the new branch's first build reports to bitbucket.

### Submitter checklist
- [ x ] Make sure you are opening from a **topic/feature/bugfix branch** (right side) and not your main branch!
- [ x ] Ensure that the pull request title represents the desired changelog entry
- [ x ] Please describe what you did
- [ x ] Link to relevant issues in GitHub or Jira
- [ x ] Link to relevant pull requests, esp. upstream and downstream changes
- [  ] Ensure you have provided tests - that demonstrates feature works or fixes the issue

[umbertix]

Is this repo maintained in any way? We are running into the same problem and we are looking into options to fix/circunvent the problem of flaky notifications.

[jninnes]

Is this repo maintained in any way? We are running into the same problem and we are looking into options to fix/circunvent the problem of flaky notifications.

Doesn’t look like it. We just built the plugin with the fix locally from my fork and deployed it manually to Jenkins.

[AndreVirtimo]

We have the same issue. There is also a Jira ticket which adress this issue: https://issues.jenkins.io/browse/JENKINS-71799