crosh: fix prompt redraws w/color

Use the \[ and \] markers around the color sequences so readline knows
which bytes are invisible.

BUG=chromium:500076
TEST=scrolling through history no longer redraws the prompt wrong

Change-Id: I6ec5518847a3e7286af955a4f3c10438897a2a61
Previous-Reviewed-on: https://chromium-review.googlesource.com/294851
(cherry picked from commit 398717de9d022792131994dfc5b3567297c44220)
Reviewed-on: https://chromium-review.googlesource.com/295970
Reviewed-by: Paul Stewart <pstew@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
1 file changed