linter fix for vm_util
linter fix for vm_util

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=278985122

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