JENKINS-60727 Add cleanSubmodule parameter to submoduleClean to add c…

[mrginglymus]

…lean a submodule's untracked submodules.

JENKINS-60727 - allow submodule clean --ffdx

#222 added the necessary plumbing for git clean -ffdx. This adds the necessary plumbing for git submodule foreach --recursive git clean -ffdx. ie., it allows you to clean a submodule's untracked submodule after updating it.

Checklist

• I have read the CONTRIBUTING doc
• I have referenced the Jira issue related to my changes in one or more commit messages
• I have added tests that verify my changes
• Unit tests pass locally with my changes
• I have added documentation as necessary
• No Javadoc warnings were introduced with my changes
• No spotbugs warnings were introduced with my changes
• I have interactively tested my changes

Types of changes

What types of changes does your code introduce? Put an x in the boxes that apply

• Infrastructure change (non-breaking change which updates dependencies or improves infrastructure)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Further comments

I appreciate that the names of the arguments aren't entirely clear - I used what was used previously for consistency but I'm not wedded to it.

[Xenoamor]

Is there any scope to merge this into master? It's a bit of a pain to have to delete my entire workspace every time and reclone everything unnecessarily