Move USB probing logic and recovery image install to servo.py.

BUG=chrome-os-partner:381
TEST=Run manually

Change-Id: I2211b7a4b24fff122e3ff6357534a89b4ab0a3ff
Reviewed-on: https://gerrit.chromium.org/gerrit/12258
Reviewed-by: Jon Salz <jsalz@chromium.org>
Tested-by: Jon Salz <jsalz@chromium.org>
Commit-Ready: Jon Salz <jsalz@chromium.org>
4 files changed