Remove target-context flags

[ulyssessouza]

As a user of the Docker App CLI tool
So that I have a consistent user experience with the Docker CLI
I want the target context flag removed

- What I did
Remove all the --target-context and references to it in the README.md

- How I did it

• removed all the --target-context and references to it in the README.md
• app is installed in context pointed by docker CLI
• installer image runs in default context by defaut until overriden by --installer-context

- How to verify it
Check the commands to see that the flags are not there anymore

- Description for the changelog
Remove target-context flags

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

[codecov]

Codecov Report

Merging #617 into master will increase coverage by 1.13%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #617      +/-   ##
==========================================
+ Coverage   70.94%   72.08%   +1.13%     
==========================================
  Files          61       61              
  Lines        3493     3374     -119     
==========================================
- Hits         2478     2432      -46     
+ Misses        695      623      -72     
+ Partials      320      319       -1

Impacted Files	Coverage Δ
internal/commands/image/list.go	83.67% <100%> (ø)	⬆️
internal/packager/init.go	61.68% <0%> (-9.13%)	⬇️
internal/commands/root.go	76.59% <0%> (-1.91%)	⬇️
internal/packager/cnab.go	97.91% <0%> (-0.09%)	⬇️
internal/names.go	100% <0%> (ø)	⬆️
internal/commands/inspect.go
internal/cliopts/installerContext.go	25% <0%> (ø)
internal/cnab/cnab.go	64.38% <0%> (+0.09%)	⬆️
internal/commands/credentials.go	70% <0%> (+0.37%)	⬆️
internal/cnab/driver.go	86.36% <0%> (+1.45%)	⬆️
... and 7 more

---

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[silvin-lubecki]

What about e2e tests https://github.com/docker/app/blob/master/e2e/commands_test.go#L480
Should we simplify them too so they stick to the user's main flow?

[kinghuang]

I strongly object to this change, assuming docker-app continues to spin up a container with the invocation image in order to do installs/uninstalls.

In my environment, it is not possible to run arbitrary containers on the swarm manager nodes. With docker-app 0.8.0, I've had to make sure that my Docker context is set to my local Docker engine (e.g., DOCKER_CONTEXT=default), and run docker-app commands with --target-context=the-remote-cluster. Otherwise, it attempts to run the invocation container on the manager node and fails.

Removing --target-context will completely break my ability to deploy apps, if an invocation container is needed. I need a way to tell docker-app to run its invocation containers in one context, and deploy to a different context.

[ulyssessouza]

@kinghuang Thank you for you feedback!
What do you think about instead of this, we use --context as the target and introducing a new experimental flag called --invocation-context?

So in your example, you could just use something like:

$ docker app install --context the-remote-cluster --invocation-context default myapp

[kinghuang]

Yes, I believe an --invocation-context option will work, and achieves the goal of consistency with the rest of the Docker CLI. An associated environment variable for the option would be greatly appreciated, too!

[silvin-lubecki]

Code looks good, but I wonder if the rm action should also have this installer context flag 🤔

[silvin-lubecki]

LGTM

[rumpl]

Couple of nits but looks good