A more robust way to set/query CPU properties on devices
A more robust way to set/query CPU properties on devices

Provides a method _ForEachCpu which runs a specified operation on
each CPU file on the device. It is efficient, as all of the commands
are executed using a single shell script on the device (as it was
already done for some of the methods); and now also more robust, as we
get the exit status of each individual command run.

BUG=433056

Review URL: https://codereview.chromium.org/732473003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#304927}

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