Fix GCP resource labels for mixed-case owner

[kiryl-filatau]

Summary

GCP rejects resource labels if they contain uppercase letters (for example owner=Name_Surname). PKB now sends lowercase labels. GCE metadata (like enable-oslogin=FALSE) is not changed.

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What broke

Running on GCP:

./pkb.py --cloud=GCP --benchmarks=kubernetes_scale

Cluster create failed:

ERROR: (gcloud.container.clusters.create) ResponseError: code=400, message=Invalid field 'resource_labels.value': 
"Name_Surname". It must only contain lowercase letters ([a-z]), numeric characters ([0-9]), underscores (_) and dashes (-). 
International characters are allowed.

Invalid field 'resource_labels.value': "Name_Surname"
(must be lowercase)

owner comes from the PKB --owner / system username and was passed to gcloud --labels without lowercasing.

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Fix

In perfkitbenchmarker/providers/gcp/util.py:

• MakeFormattedDefaultTags() → add .lower() (used for GCP --labels)
• FormatTags() → no change (used for GCE --metadata)

One unit test: testMakeFormattedDefaultTagsLowercasesOwner.

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How was tested

• python3 -m pytest tests/providers/gcp/util_test.py::GcpUtilTest tests/providers/gcp/gce_managed_instance_group_test.py -v
• ./pkb.py --cloud=GCP --benchmarks=kubernetes_scale — cluster create works, labels are lowercase