Split cluster package into multiple files

[tstromberg]

No functionality change: just splitting a gigantic file up to prepare for fixing #6479

[k8s-ci-robot]

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This pull-request has been approved by: tstromberg

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[medyagh]

Thanks for making it easier to read the code

[tstromberg]

/ok-to-test

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@bb539cb). Click here to learn what that means.
The diff coverage is 62.22%.

@@            Coverage Diff            @@
##             master    #6484   +/-   ##
=========================================
  Coverage          ?   37.81%           
=========================================
  Files             ?      138           
  Lines             ?     8745           
  Branches          ?        0           
=========================================
  Hits              ?     3307           
  Misses            ?     5017           
  Partials          ?      421

Impacted Files	Coverage Δ
pkg/minikube/cluster/delete.go	37.5% <ø> (ø)
pkg/minikube/cluster/stop.go	25% <ø> (ø)
pkg/minikube/cluster/cluster.go	50% <ø> (ø)
pkg/minikube/cluster/docker_env.go	61.9% <ø> (ø)
pkg/minikube/cluster/ip.go	0% <ø> (ø)
pkg/minikube/cluster/iso.go	0% <ø> (ø)
pkg/minikube/cluster/status.go	36.36% <ø> (ø)
pkg/minikube/cluster/info.go	31.37% <ø> (ø)
pkg/minikube/cluster/ssh.go	42.85% <ø> (ø)
pkg/minikube/cluster/start.go	47.82% <ø> (ø)
... and 3 more

[minikube-pr-bot]

All Times Minikube (PR 6484): [ 99.676328 99.116067 94.824221]
All Times minikube: [ 98.082614 97.283176 100.029719]

Average Minikube (PR 6484): 97.872205
Average minikube: 98.465170

Averages Time Per Log

+----------------------+-----------+--------------------+
|         LOG          | MINIKUBE  | MINIKUBE (PR 6484) |
+----------------------+-----------+--------------------+
| minikube v           |  0.325515 |           0.293104 |
| Creating kvm2        | 20.311569 |          20.422813 |
| Preparing Kubernetes | 51.117875 |          50.675088 |
| Pulling images       |  3.866258 |           3.665200 |
| Launching Kubernetes | 19.840260 |          19.250372 |
| Waiting for cluster  |  1.409745 |           1.553541 |
+----------------------+-----------+--------------------+