tunnel on docker driver on mac: fix known_hosts issue

[josedonizetti]

fix for #6809

[k8s-ci-robot]

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[codecov-io]

Codecov Report

Merging #6810 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6810      +/-   ##
==========================================
- Coverage    38.5%   38.49%   -0.02%     
==========================================
  Files         142      142              
  Lines        8695     8698       +3     
==========================================
  Hits         3348     3348              
- Misses       4927     4930       +3     
  Partials      420      420

Impacted Files	Coverage Δ
pkg/minikube/machine/start.go	53.84% <0%> (-1.16%)	⬇️