fix(unit test): add mock

[hecomlilong]

What type of PR is this?

error fix

What this PR does / why we need it:

fix cluster_test error when execute command 'make test'

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

[github-actions]

🎉 Successfully Build Images.

Overview: https://finops.coding.net/public-artifacts/gocrane/crane/packages

Image	Pull Command
crane-agent:pr-298-477d61b	docker pull finops-docker.pkg.coding.net/gocrane/crane/crane-agent:pr-298-477d61b
dashboard:pr-298-477d61b	docker pull finops-docker.pkg.coding.net/gocrane/crane/dashboard:pr-298-477d61b
metric-adapter:pr-298-477d61b	docker pull finops-docker.pkg.coding.net/gocrane/crane/metric-adapter:pr-298-477d61b
craned:pr-298-477d61b	docker pull finops-docker.pkg.coding.net/gocrane/crane/craned:pr-298-477d61b

[kitianFresh]

/LGTM