Fix issue 1981

[hirsim]

Fix issue /issues/1981.

Path to the cert file in /var/lib/localkube/kubeconfig on a minikube VM was broken.

apiVersion: v1
clusters:
- cluster:
    certificate-authority: \var\lib\localkube\certs\ca.crt
    server: https://localhost:8443
  name: minikube
contexts:
- context:
    cluster: minikube
    user: minikube
  name: minikube
current-context: minikube
kind: Config
preferences: {}
users:
- name: minikube
  user:
    client-certificate: \var\lib\localkube\certs\apiserver.crt
    client-key: \var\lib\localkube\certs\apiserver.key

Fixed it.

And fixed create location of a image cache folder for Windows.
But, ParseReference does not support Windows drive letter.
If contains Windows drive letter, it disable caching image for now.

[minikube-bot]

Can one of the admins verify this patch?

[r2d4]

@minikube-bot ok to test

[codecov-io]

Codecov Report

Merging #1982 into master will decrease coverage by 0.12%.
The diff coverage is 16.66%.

@@            Coverage Diff             @@
##           master    #1982      +/-   ##
==========================================
- Coverage      30%   29.87%   -0.13%     
==========================================
  Files          77       77              
  Lines        4740     4760      +20     
==========================================
  Hits         1422     1422              
- Misses       3138     3158      +20     
  Partials      180      180

Impacted Files	Coverage Δ
pkg/minikube/machine/cache_images.go	2.18% <0%> (-0.38%)	⬇️
pkg/minikube/bootstrapper/certs.go	85.6% <100%> (ø)	⬆️

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[r2d4]

Thanks!