autotest: servo: Re-work keypress for servo V2

CL gets keypress automation working for servo V2.  See deps commit msg
for more details.

Additionally,
1. Adds the method for ctrl_enter keypress.  See crosbug.com/p/6759
for details.
2. Sets kbd row & columns to none state each time prior to enabling to
guarantee more uniform key triggering.
3. Remove hard-coded config default, 'servo.xml' as servod daemon can
determine which to load via the USB iSerial programmed on the servo
board
4. bug fix for invoking servod via popen.
5. General cleanup of pylint warnings

CQ-DEPEND=I88706ed3dc6f7787fe909c51ef222c969657494a
BUG=none
TEST=manual, wrote small 'throw away' test to invoke keypresses and
inspect them working on both servo V1 & servo V2 interactively

Change-Id: I15fbee5f294c5df3896a07c9d9be8169a36aea32
Reviewed-on: https://gerrit.chromium.org/gerrit/18747
Commit-Ready: Todd Broch <tbroch@chromium.org>
Reviewed-by: Todd Broch <tbroch@chromium.org>
Tested-by: Todd Broch <tbroch@chromium.org>
1 file changed