ktop now drains the ring buffer

Before beginning to collect data, ktop now drains the per cpu ring buffers.
Also fixed a couple of problems in dumping the ring buffers while testing.

BUG=chromium-os:38503
TEST=ran on stumpy

Change-Id: I3fce487ce4dab6df1f1ff34d1b401ba2d258472d
Reviewed-on: https://gerrit.chromium.org/gerrit/42675
Tested-by: Paul Taysom <taysom@chromium.org>
Reviewed-by: Luigi Semenzato <semenzato@chromium.org>
Commit-Queue: Paul Taysom <taysom@chromium.org>
3 files changed