Tweak CPU support; list all available CPU frequencies.

Tweak CPU support; list all available CPU frequencies.

This is only exposed on newer kernels, so extract the old values on older
kernels.

Use stricter checking in SetCPUSpeed().

R=stip@chromium.org
BUG=chromium:525873
Committed: https://github.com/luci/luci-py/commit/9beaef81eb32a0e412ac9dfe1157f67b75fd570b

[ghost stip (do not use), 2015-11-04 21:05:10]

lgtm

[M-A Ruel, 2015-11-04 21:08:59]

The CQ bit was checked by maruel@chromium.org

[commit-bot: I haz the power, 2015-11-04 21:09:03]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-11-04 21:09:03]

This CL has an open dependency (Issue 1424923006 Patch 60001). Please resolve
the dependency and try again.

[M-A Ruel, 2015-11-05 12:05:09]

Patchset #4 (id:60001) has been deleted

[M-A Ruel, 2015-11-05 12:07:18]

Patchset #4 (id:80001) has been deleted

[M-A Ruel, 2015-11-05 15:53:00]

Patchset #4 (id:100001) has been deleted

[M-A Ruel, 2015-11-05 15:53:09]

Patchset #4 (id:120001) has been deleted

[M-A Ruel, 2015-11-05 20:43:49]

The CQ bit was checked by maruel@chromium.org

[M-A Ruel, 2015-11-05 20:43:49]

The patchset sent to the CQ was uploaded after l-g-t-m from stip@chromium.org
Link to the patchset: https://codereview.chromium.org/1421463006/#ps140001
(title: "Remove freqs, it's noisy in swarming stats and already available")

[commit-bot: I haz the power, 2015-11-05 20:44:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1421463006/140001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1421463006/140001

[commit-bot: I haz the power, 2015-11-05 20:45:07]

Committed patchset #4 (id:140001) as
https://github.com/luci/luci-py/commit/9beaef81eb32a0e412ac9dfe1157f67b75fd570b