Kubernetes tests simplify build creation

In the kubernetes tests we currently have a lot of copy-paste build definitions, such as:

&common.Build{
		JobResponse: jobResponse,
		Runner: &common.RunnerConfig{
			RunnerSettings: common.RunnerSettings{
				Executor: "kubernetes",
				Kubernetes: &common.KubernetesConfig{
					PullPolicy: common.PullPolicyIfNotPresent,
					PodLabels: map[string]string{
						"test.k8s.gitlab.com/name": podUUID,
					},
				},
			},
		},
	}

We should simplify them by reusing the introduced in !2444 (merged) function getTestBuild