[Failing test] guestbook test is failing on azure with K8s v1.21.0

[ialidzhikov]

How to categorize this issue?

/area testing
/kind bug
/priority 2
/platform azure

How to reproduce it (as minimally and precisely as possible):

1. Run the guestbook test against azure K8s v1.21.0

go test -timeout=0 -mod=vendor ./test/suites/shoot \
      --v -ginkgo.v -ginkgo.progress -ginkgo.noColor \
      --report-file=/tmp/report.json \
      -kubecfg=$KUBECONFIG \
      -shoot-name=$SHOOT_NAME \
      -project-namespace=$PROJECT_NAMESPACE \
      -ginkgo.focus="should deploy guestbook app successfully"

2. Make sure that redis-master-0 is in CrashLoopBackOff and the test fails because of it

$ k -n gardener-e2e-6r26f get po
NAME             READY   STATUS             RESTARTS   AGE
redis-master-0   0/1     CrashLoopBackOff   5          4m21s

$ k -n gardener-e2e-6r26f get pvc
NAME                        STATUS   VOLUME                                                         CAPACITY   ACCESS MODES   STORAGECLASS   AGE
redis-data-redis-master-0   Bound    pv-shoot--fooooooo--test-b95ceb44-ac8f-427d-bbd8-576596e6c23   8Gi        RWO            default        5m8s

$ k -n gardener-e2e-6r26f logs redis-master-0 -p
 10:41:33.23 INFO  ==> ** Starting Redis **
1:C 13 May 2021 10:41:33.238 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
1:C 13 May 2021 10:41:33.238 # Redis version=5.0.7, bits=64, commit=00000000, modified=0, pid=1, just started
1:C 13 May 2021 10:41:33.238 # Configuration loaded
1:M 13 May 2021 10:41:33.238 # Can't open the append-only file: Permission denied

Environment:

• Gardener version (if relevant): v1.23.0-dev-b48ae95e29853f7bb590c6838b4e2aa70c6c98d2
• Extension version: v1.20.0-dev-ed3f9485ca0d4c581218d3ccc244b542e5daa78c
• Kubernetes version (use kubectl version): v1.21.0
• Cloud provider or hardware configuration:
• Others:

[ialidzhikov]

/cc @rfranzke @dguendisch @kon-angelo

[ialidzhikov]

[ialidzhikov]

It looks similar to gardener/gardener-extension-provider-openstack#142
I am going to grab some food, and will test the fix after it.