Missing cache key in log messages (workspace open)

Summary

During bst workspace open, various messages do not contain the associated elements cache key.

Steps to reproduce

Open a workspace, observe output.

What is the current bug behavior?

Messages are produced without any cache key

What is the expected correct behavior?

All messages associated with the operation triggered for the element should contain its cache key.

Relevant logs and/or screenshots

[--:--:--][651aa7ef][ main:5G.bst                        ] START   Staging sources to /home/joshsmith/buildstream/doc/examples/CAS-interaction/wspdir
[--:--:--][        ][ main:5G.bst-0                      ] STATUS  Running host command

    /usr/bin/git show 72b5902157316e173de2eec5b3a2772283eec3c7:.gitmodules

[--:--:--][        ][ main:5G.bst-0                      ] START   Setting up workspace "/home/joshsmith/.cache/buildstream/build/workspace-5Gr52jkhma"
[00:00:00][        ][ main:5G.bst-0                      ] SUCCESS Setting up workspace "/home/joshsmith/.cache/buildstream/build/workspace-5Gr52jkhma"
[00:00:00][651aa7ef][ main:5G.bst                        ] SUCCESS Staging sources to /home/joshsmith/buildstream/doc/examples/CAS-interaction/wspdir
[--:--:--][][] INFO    Saved workspace configuration

Other relevant information

• BuildStream version affected: master @ 7dd74b01

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