Add GCE COS unit test to catch weird edge cases with the OS.
Add GCE COS unit test to catch weird edge cases with the OS.

PiperOrigin-RevId: 324710340

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