fix(provider): improve recognition of exit codes (backport #135)

[mergify]

currently, both DO and Docker providers do not wait for the container to exit until returning an exit code. this introduces a condition, where the container hasn't exited yet (e.g. with an error), but we already fetch it's stdout and exit code (which at that point is 0). this commit makes the providers wait for the exec container to finish and only then returns the response.

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This is an automatic backport of pull request #135 done by Mergify.

[mergify]

Cherry-pick of 4a67052 has failed:

On branch mergify/bp/release/v2.x.x/pr-135
Your branch is up to date with 'origin/release/v2.x.x'.

You are currently cherry-picking commit 4a67052.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   cosmos/node/genesis.go
	modified:   cosmos/node/keys.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   core/provider/digitalocean/task.go
	both modified:   core/provider/docker/task.go
	both modified:   cosmos/node/init.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally