util: Add EC-3PO, the EC console interpreter.

EC-3PO is the console interpreter that will one day replace the EC console
that we have today.  EC-3PO aims to migrate our rich debug console from
the EC itself to the host.  This allows us to maintain our rich debug
console without impacting our EC image sizes while also allowing us to
add new features.

This commit is the 1st of three phases, the insertion phase.  The main
goal of this insertion phase is to get EC-3PO in place between servo and
the EC UART, while not modifying the behaviour of the console too
much.  At this point, EC-3PO is capable of the following things:

 - Replicate command editing.
 - Save command history.
 - Performs error checking with console commands.

The command editing should be at parity with the current EC console.
With EC-3PO, one can have a much longer command history which also
persists across EC reboots. And lastly, with a cooperating EC image,
EC-3PO can perform error checking with console commands.  Automatically
retrying console commands if the command was incorrectly received at the
EC end.

Currently, commands are sent to the EC in a "packed" plaintext form.
The next phase will introduce the host command packet communication.

console.py is the module that provides the console interface between the
user and the interpreter.  It handles the presentation of the console
including command editing.

It also has an accompanying set of unit tests in console_unittest.py.
It currently has 1 test suite to test the various console editing
methods.

interpreter.py is the module that provides the interpretation layer
between the EC and the user.  It also is responsible for the automatic
command retrying.  It requires pipe connections to be made to it for
command and debug data communication.

BUG=chrome-os-partner:46054
BRANCH=None
TEST=util/ec3po/console_unittest.py
TEST=Flash GLaDOS with a modified EC build.  Run console.py passing the
EC UART, verify that I can edit commands, send commands, view command
history, and receive output from the EC.
TEST=cros lint --log-level debug ./util/ec3po/console.py
TEST=cros lint --log-level debug ./util/ec3po/interpreter.py
TEST=cros lint --log-level debug ./util/ec3po/console_unittest.py

Change-Id: I38ae425836efd69044334e1ed0daf3f88a95917c
Signed-off-by: Aseda Aboagye <aaboagye@google.com>
Reviewed-on: https://chromium-review.googlesource.com/308615
Commit-Ready: Aseda Aboagye <aaboagye@chromium.org>
Tested-by: Aseda Aboagye <aaboagye@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Reviewed-by: Wai-Hong Tam <waihong@chromium.org>

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