docker-env & podman-env: silent output when talking to a shell

[afbjorklund]

If the output is not a terminal, then assume that we are running
docker-env or podman-env under "eval" or similar shell construct.

So don't output all the interactive information, but only return
the actual exit code for some further troubleshooting (perhaps).

Closes #10761

---

BEFORE

$ eval $(minikube docker-env)
🤷: command not found
$ minikube docker-env
🤷  The control plane node must be running for this command
👉  To start a cluster, run: "minikube start"

or, even worse:

$ export MINIKUBE_IN_STYLE=false
$ eval $(minikube docker-env)
CHANGELOG.md: command not found
$ minikube docker-env
* The control plane node must be running for this command
  - To start a cluster, run: "minikube start"

AFTER

$ eval $(minikube docker-env)
$
$ minikube docker-env
🤷  The control plane node must be running for this command
👉  To start a cluster, run: "minikube start"

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[medyagh]

@afbjorklund could u plz post the before and after this PR in description ?

I think this worth an integration test, how about adding one in the DockerEnv Test?

[afbjorklund]

@afbjorklund could u plz post the before and after this PR in description ?

Already done, see #10761 (comment)

[medyagh]

I think adding an integraiton test will ensure we will never break this

how about adding one here in validateDockerEnv
https://github.com/medyagh/minikube/blob/8da592988da45acfc93cef2637e79a8bfa4ad570/test/integration/functional_test.go#L216

[medyagh]

/ok-to-test

[minikube-pr-bot]

kvm2 Driver
error collecting results for kvm2 driver: timing run 0 with Minikube (PR 10763): timing cmd: [/home/performance-monitor/.minikube/minikube-binaries/10763/minikube start --driver=kvm2]: starting cmd: fork/exec /home/performance-monitor/.minikube/minikube-binaries/10763/minikube: exec format error
docker Driver
error collecting results for docker driver: timing run 0 with Minikube (PR 10763): timing cmd: [/home/performance-monitor/.minikube/minikube-binaries/10763/minikube start --driver=docker]: starting cmd: fork/exec /home/performance-monitor/.minikube/minikube-binaries/10763/minikube: exec format error