prow.sh: collect cluster logs

We create at most two different clusters for each job, one with alpha
features enabled and one without. For both the logs of system
components are collected before tearing down the cluster and stored as
artifacts under "cluster-logs/[non-]alpha".

This is useful in particular for kubelet logs.

prow.sh

@@ -621,11 +621,16 @@ EOF
 
 # Deletes kind cluster inside a prow job
 delete_cluster_inside_prow_job() {
+    local name="$1"
+
     # Inside a real Prow job it is better to clean up at runtime
     # instead of leaving that to the Prow job cleanup code
     # because the later sometimes times out (https://github.com/kubernetes-csi/csi-release-tools/issues/24#issuecomment-554765872).
+    #
+    # This is also a good time to collect logs.
     if [ "$JOB_NAME" ]; then
         if kind get clusters | grep -q csi-prow; then
+            run kind export logs --name=csi-prow "${ARTIFACTS}/cluster-logs/$name"
             run kind delete cluster --name=csi-prow || die "kind delete failed"
         fi
         unset KUBECONFIG
@@ -1210,7 +1215,7 @@ main () {
                     fi
                 fi
             fi
-            delete_cluster_inside_prow_job
+            delete_cluster_inside_prow_job non-alpha
         fi
 
         if tests_need_alpha_cluster && [ "${CSI_PROW_E2E_ALPHA_GATES}" ]; then
@@ -1245,7 +1250,7 @@ main () {
                     fi
                 fi
             fi
-            delete_cluster_inside_prow_job
+            delete_cluster_inside_prow_job alpha
         fi
     fi