feat: add use-local-cached-images option.

[Colstuwjx]

This PR is going to fixes #6103 by introducing a new config option use-local-cached-images, it will load local cached images without fetching images, and make minikube works well inside no-public-network-access environment.

[minikube-bot]

Can one of the admins verify this patch?

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Colstuwjx
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[Colstuwjx]

BTW, on my laptop, I still could see some error messages output for kubeadm related issue while execute ./out/minikube start --memory=8196 --cpus=4 --use-local-cached-images, maybe it would be another PR to fix, the errors see below:

😄  Darwin 10.14.6 上的 minikube v1.6.1
✨  Selecting 'virtualbox' driver from user configuration (alternates: [hyperkit])
🔥  正在创建 virtualbox 虚拟机（CPUs=4，Memory=8196MB, Disk=20000MB）...
⚠️  VM is unable to access k8s.gcr.io, you may need to configure a proxy or set --image-repository
🐳  正在 Docker '19.03.5' 中准备 Kubernetes v1.17.0…
🚜  拉取镜像 ...
❌  无法拉取映像，有可能是正常状况：running cmd: "/bin/bash -c \"sudo env PATH=/var/lib/minikube/binaries/v1.17.0:$PATH kubeadm config images pull --config /var/tmp/minikube/kubeadm.yaml\"": /bin/bash -c "sudo env PATH=/var/lib/minikube/binaries/v1.17.0:$PATH kubeadm config images pull --config /var/tmp/minikube/kubeadm.yaml": Process exited with status 1
stdout:

stderr:
W1217 13:10:41.291378    3250 common.go:77] your configuration file uses a deprecated API spec: "kubeadm.k8s.io/v1beta1". Please use 'kubeadm config migrate --old-config old.yaml --new-config new.yaml', which will write the new, similar spec using a newer API version.
W1217 13:10:41.291968    3250 common.go:77] your configuration file uses a deprecated API spec: "kubeadm.k8s.io/v1beta1". Please use 'kubeadm config migrate --old-config old.yaml --new-config new.yaml', which will write the new, similar spec using a newer API version.
W1217 13:10:41.295286    3250 validation.go:28] Cannot validate kube-proxy config - no validator is available
W1217 13:10:41.295309    3250 validation.go:28] Cannot validate kubelet config - no validator is available
failed to pull image "k8s.gcr.io/kube-apiserver:v1.17.0": output: Error response from daemon: Get https://k8s.gcr.io/v2/: net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
, error: exit status 1
To see the stack trace of this error execute with --v=5 or higher

🚀  正在启动 Kubernetes ...
⌛  Waiting for cluster to come online ...
🏄  完成！kubectl 已经配置至 "minikube"

[codecov-io]

Codecov Report

Merging #6105 into master will increase coverage by <.01%.
The diff coverage is 27.27%.

@@            Coverage Diff             @@
##           master    #6105      +/-   ##
==========================================
+ Coverage    36.7%   36.71%   +<.01%     
==========================================
  Files         113      113              
  Lines        8355     8361       +6     
==========================================
+ Hits         3067     3070       +3     
- Misses       4887     4890       +3     
  Partials      401      401

Impacted Files	Coverage Δ
pkg/minikube/machine/cache_images.go	4.36% <0%> (-0.02%)	⬇️
pkg/minikube/driver/driver.go	92.72% <100%> (+0.13%)	⬆️
cmd/minikube/cmd/start.go	22.82% <50%> (+0.15%)	⬆️

[tstromberg]

Offline support is supposed to work by default without user intervention, so I would prefer to not add a flag unless necessary.

#6111 should also rectify the issue.

[Colstuwjx]

Yes, I agree.