Add --override-os-version to telemetry for decorators

telemetry/telemetry/internal/platform/linux_platform_backend.py

Index: telemetry/telemetry/internal/platform/linux_platform_backend.py
diff --git a/telemetry/telemetry/internal/platform/linux_platform_backend.py b/telemetry/telemetry/internal/platform/linux_platform_backend.py
index ba1d82ccfcb4b69c104d99fa63d2c72118600607..d09380dc4181ae57e615bf4f678ffd1f5231dc22 100644
--- a/telemetry/telemetry/internal/platform/linux_platform_backend.py
+++ b/telemetry/telemetry/internal/platform/linux_platform_backend.py
@@ -31,6 +31,7 @@ class LinuxPlatformBackend(
   def __init__(self):
     super(LinuxPlatformBackend, self).__init__()
     self._power_monitor = msr_power_monitor.MsrPowerMonitorLinux(self)
+    self.override_os_version = None
 
   @classmethod
   def IsPlatformBackendForHost(cls):
@@ -51,6 +52,9 @@ class LinuxPlatformBackend(
 
   @decorators.Cache
   def GetOSVersionName(self):
+    if self.override_os_version:
+      return self.override_os_version
+
     if not os.path.exists('/etc/lsb-release'):
       raise NotImplementedError('Unknown Linux OS version')