Python3 migration fix: Default "wb+" mode expects bytes-like object.
Python3 migration fix: Default "wb+" mode expects bytes-like object.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=268314193

GoogleCloudPlatform/PerfKitBenchmarker,GoogleCloudPlatform/PerfKitBenchmarker,GoogleCloudPlatform/PerfKitBenchmarker,GoogleCloudPlatform/PerfKitBenchmarker