fix: config dir default empty

[lkingland]

🐛 fix incorrect default config directory
🐛 add a clean home setup to a test

When the system can not automatically determine a determine a config directory path, it should communicate this by returning the zero value, letting the caller handle the situation accordingly (skip usage, or create a temporary home directory)

/kind bug

Related: #901

[knative-prow]

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[codecov]

Codecov Report

Base: 53.50% // Head: 62.20% // Increases project coverage by +8.70% 🎉

Coverage data is based on head (3bcc66c) compared to base (3665769).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1376      +/-   ##
==========================================
+ Coverage   53.50%   62.20%   +8.70%     
==========================================
  Files          72       75       +3     
  Lines       10477    10598     +121     
==========================================
+ Hits         5606     6593     +987     
+ Misses       4443     3449     -994     
- Partials      428      556     +128     

Flag	Coverage Δ
integration-tests	51.88% <100.00%> (?)
unit-tests-macos-latest	52.05% <100.00%> (?)
unit-tests-ubuntu-latest	53.48% <100.00%> (?)
unit-tests-windows-latest	52.07% <100.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
config/config.go	94.54% <100.00%> (-0.46%)	⬇️
openshift/openshift.go	5.76% <0.00%> (ø)
openshift/metadata.go	0.00% <0.00%> (ø)
docker/docker_client_nonlinux.go	0.00% <0.00%> (ø)
client.go	63.75% <0.00%> (+0.62%)	⬆️
docker/creds/credentials.go	73.06% <0.00%> (+1.34%)	⬆️
k8s/secrets.go	19.58% <0.00%> (+6.18%)	⬆️
k8s/configmaps.go	50.00% <0.00%> (+15.78%)	⬆️
k8s/client.go	88.46% <0.00%> (+23.07%)	⬆️
docker/docker_client.go	84.87% <0.00%> (+25.21%)	⬆️
... and 11 more

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[matejvasek]

/lgtm