Command Id instead of class & method id

[bollhals]

Proposed Changes

This is a follow up on #924 / #877
This was one change that I wanted to add as a separate PR to not mix it up. Changed originally as part of #877

Types of Changes

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

• Bug fix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

Further Comments

This is on top of #924 , so the actual change is only within commit: 5f4f47e

[stebet]

I've also done this in the full-async branch. If there is code there you can borrow as well, please do :)