use NSM_KUBERNETES_VERSION variable to specify k8s version for clusters #723

Job	Run time
interdomain	11m 40s
yamllint / yamllint	10s
golangci-lint / golangci-lint	31s
checkgomod / checkgomod	11s
exclude-fmt-errorf / exclude-fmt-errorf	5s
shellcheck / shellcheck	13s
	12m 50s

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