deploy_id should be based on branch, not stage

Hi,

In our project we have multiple deploy targets we send our application to. Using this plugin this means for each of the targets a new build gets made. It's not a huge hassle, but it does waste some time.

One of the issues is with how the deploy_id is made. Today it consists out of the app name (application), stage, repo_url and working directory.

I'd like to start a discussion about this. I think it would be more valuable to have the stage be replaced with the branch_name or the sha of the branch reference.

This has some benefits.

• No impact if a stage is renamed
• Stages using the same branch can use the same archive (if we optimise that)

If there is support for this, I would be happy to make a PR. Happy to hear your feedback!