Fix docker-env and add unit and integration tests

[medyagh]

Added both unit and integration tests for docker-env command.

test with both docker and kvm driver

Before this PR:

export DOCKER_TLS_VERIFY="1"
export DOCKER_HOST="tcp://172.17.0.2:2376"
export DOCKER_CERT_PATH="tcp://127.0.0.1:32874"
export MINIKUBE_ACTIVE_DOCKERD="minikube"

# To point your shell to minikube's docker-daemon, run:
# eval $(minikube -p minikube docker-env)

After this PR :

export DOCKER_TLS_VERIFY="1"
export DOCKER_HOST="tcp://127.0.0.1:32841"
export DOCKER_CERT_PATH="/usr/local/google/home/medya/.minikube/certs"
export MINIKUBE_ACTIVE_DOCKERD="minikube"

# To point your shell to minikube's docker-daemon, run:
# eval $(minikube -p minikube docker-env)

closes #6600
closes #6546

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: medyagh

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [medyagh]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[tstromberg]

Do you mind adding a docker entry to env_test.go?

[tstromberg]

Also, is there an integration test that runs docker ps against what is returned? Even if it's just bash-specific, it would be nice to catch this.

[medyagh]

/ok-to-test

[tstromberg]

Lint failure:

test/integration/functional_test.go:138:2: SA4006: this value of `rr` is never used (staticcheck)
300	rr, err = Run(t, c)
301	^
302Makefile:369: recipe for target 'lint-ci' failed

[minikube-pr-bot]

All Times minikube: [ 95.833955 91.993915 93.698440]
All Times Minikube (PR 6604): [ 91.871670 94.387630 94.758049]

Average minikube: 93.842103
Average Minikube (PR 6604): 93.672450

Averages Time Per Log

+----------------------+-----------+--------------------+
|         LOG          | MINIKUBE  | MINIKUBE (PR 6604) |
+----------------------+-----------+--------------------+
| minikube v           |  0.200996 |           0.203549 |
| Creating kvm2        | 19.718525 |          19.888721 |
| Preparing Kubernetes | 50.093373 |          50.248404 |
| Pulling images       |           |                    |
| Launching Kubernetes | 21.457886 |          21.508697 |
| Waiting for cluster  |  0.051724 |           0.050020 |
+----------------------+-----------+--------------------+

[medyagh]

fixed lint

[minikube-pr-bot]

All Times minikube: [ 94.454109 92.421270 91.599450]
All Times Minikube (PR 6604): [ 92.350928 90.824207 91.032529]

Average minikube: 92.824943
Average Minikube (PR 6604): 91.402555

Averages Time Per Log

+----------------------+-----------+--------------------+
|         LOG          | MINIKUBE  | MINIKUBE (PR 6604) |
+----------------------+-----------+--------------------+
| minikube v           |  0.197200 |           0.208009 |
| Creating kvm2        | 19.893442 |          19.610107 |
| Preparing Kubernetes | 50.159653 |          49.293271 |
| Pulling images       |           |                    |
| Launching Kubernetes | 20.513365 |          20.350200 |
| Waiting for cluster  |  0.068647 |           0.223605 |
+----------------------+-----------+--------------------+

[codecov-io]

Codecov Report

Merging #6604 into master will not change coverage.
The diff coverage is 36.36%.

@@           Coverage Diff           @@
##           master    #6604   +/-   ##
=======================================
  Coverage   37.51%   37.51%           
=======================================
  Files         138      138           
  Lines        8792     8792           
=======================================
  Hits         3298     3298           
- Misses       5078     5080    +2     
+ Partials      416      414    -2

Impacted Files	Coverage Δ
cmd/minikube/cmd/docker-env.go	39.83% <36.36%> (ø)	⬆️

[minikube-pr-bot]

All Times minikube: [ 92.883412 87.392601 90.922051]
All Times Minikube (PR 6604): [ 97.037286 94.931300 94.773415]

Average minikube: 90.399354
Average Minikube (PR 6604): 95.580667

Averages Time Per Log

+----------------------+-----------+--------------------+
|         LOG          | MINIKUBE  | MINIKUBE (PR 6604) |
+----------------------+-----------+--------------------+
| minikube v           |  0.225134 |           0.198086 |
| Creating kvm2        | 20.170219 |          20.171272 |
| Preparing Kubernetes | 48.026547 |          51.366552 |
| Pulling images       |           |                    |
| Launching Kubernetes | 20.000610 |          21.891226 |
| Waiting for cluster  |  0.219855 |           0.241984 |
+----------------------+-----------+--------------------+

[minikube-pr-bot]

All Times minikube: [ 91.279304 94.006040 93.822893]
All Times Minikube (PR 6604): [ 91.536026 93.898284 92.012377]

Average minikube: 93.036079
Average Minikube (PR 6604): 92.482229

Averages Time Per Log

+----------------------+-----------+--------------------+
|         LOG          | MINIKUBE  | MINIKUBE (PR 6604) |
+----------------------+-----------+--------------------+
| minikube v           |  0.206499 |           0.202772 |
| Creating kvm2        | 20.183795 |          20.151431 |
| Preparing Kubernetes | 49.940577 |          49.854166 |
| Pulling images       |           |                    |
| Launching Kubernetes | 20.956622 |          20.412887 |
| Waiting for cluster  |  0.046799 |           0.224631 |
+----------------------+-----------+--------------------+