Reorder cluster shutdown to reflect the reverse order of startup

[jstnlef]

Description

I also added a mechanism for calling code to await the completion of cluster shutdown. This should allow for a smoother shutdown w.r.t. any provider registration/deregistration code.

Purpose

This pull request is a:

• Bugfix (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)

Checklist

• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)