Fix and re-enable BstatsCpuTimesValidationTest

Thanks to jji@ for identifying the cause and the fix.

Bug: 180015146
Test: atest FrameworksCoreTests:com.android.internal.os.BstatsCpuTimesValidationTest
BYPASS_INCLUSIVE_LANGUAGE_REASON=Using a legacy command, cmd deviceidle whitelist

Change-Id: I1dd2402719d5ae7752300b72a5afe3740ac7498a