Skip removing USB on recovery-button-triggered boot when dev switch off.

We added an optimization and changed this behevior on recent models.
In summary,
    when dev_mode ON, directly boot to USB stick if presented;
    when dev_mode OFF,
        the old models need users to remove and insert the USB;
        the new models directly boot to the USB.

BUG=chrome-os-partner:7306;chromium-os:19710
TEST=tested on old and new devices.
$ run_remote_tests.sh --remote=$REMOTE_IP -a "xml_config=$OVERLAY_XML \
      servo_vid=0x18d1 servo_pid=0x5001" RecoveryButton/control.normal

Change-Id: I22803e3d6616bf678916ed1877589e0583575d3d
Reviewed-on: https://gerrit.chromium.org/gerrit/13315
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
Commit-Ready: Tom Wai-Hong Tam <waihong@chromium.org>
Tested-by: Tom Wai-Hong Tam <waihong@chromium.org>
1 file changed