Consistent object naming in usage command and examples

[carolinebriaud]

Signed-off-by: Caroline Briaud caroline.briaud@docker.com

- What I did
Correct help messages, examples and flag descriptions to match the app naming rules

- How to verify it
Go through help, examples and flag description for each docker app command

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

[codecov]

Codecov Report

Merging #704 into master will decrease coverage by 1.01%.
The diff coverage is 95.52%.

@@            Coverage Diff            @@
##           master    #704      +/-   ##
=========================================
- Coverage   72.21%   71.2%   -1.02%     
=========================================
  Files          59      59              
  Lines        3146    2997     -149     
=========================================
- Hits         2272    2134     -138     
  Misses        580     580              
+ Partials      294     283      -11

Impacted Files	Coverage Δ
internal/commands/pull.go	69.23% <100%> (ø)	⬆️
internal/commands/init.go	86.66% <100%> (ø)	⬆️
internal/commands/image/inspect.go	74.46% <100%> (-4.48%)	⬇️
internal/commands/render.go	70.9% <100%> (ø)	⬆️
internal/commands/image/tag.go	88.88% <100%> (-2.61%)	⬇️
internal/commands/image/list.go	83.33% <100%> (-4.17%)	⬇️
internal/commands/remove.go	52% <100%> (ø)	⬆️
internal/commands/image/rm.go	62.5% <100%> (-1.61%)	⬇️
internal/commands/list.go	84.12% <100%> (ø)	⬆️
internal/commands/root.go	75% <100%> (ø)	⬆️
... and 13 more

---

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[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "fix-usages-examples" git@github.com:carolinebriaud/app.git somewhere
$ cd somewhere
$ git rebase -i HEAD~842354382296
editor opens
change each 'pick' to 'edit'
save the file and quit
$ git commit --amend -s --no-edit
$ git rebase --continue # and repeat the amend for each commit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[eunomie]

I'm not sure about some changes around brackets.
A very common pattern in CLI help is to mark optional fields between brackets and to avoid brackets on all mandatory fields. That way it's easy to know what to provide.

[silvin-lubecki]

@carolinebriaud can you rebase this PR?

[chris-crone]

One minor change but then LGTM

[chris-crone]

LGTM

[silvin-lubecki]

LGTM