list/tree: Hide Used column if no truthy value

[vvoland]

• stacked on: https://github.com/docker/cli/pull/5356

Don't show the Used column in the image tree view when no image is actually used and the column would be empty.

- A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 60.90%. Comparing base (0be9e2f) to head (54a4ab1). Report is 486 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5357      +/-   ##
==========================================
- Coverage   60.92%   60.90%   -0.02%     
==========================================
  Files         304      304              
  Lines       21340    21345       +5     
==========================================
  Hits        13001    13001              
- Misses       7409     7414       +5     
  Partials      930      930              

[krissetto]

I'm not totally sure about this from a UX perspective.. wouldn't it risk being a bit confusing for the users if sometimes they see the column and sometimes they don't?

[laurazard]

I'm fine with it for now since this is behind an experimental flag, but we should review these questions before making it stable.