python: Convert terminal escape sequences to strings.

python: Convert terminal escape sequences to strings.

In python 3, the curses escape sequences are bytes objects and not
strings, making them unsuitable to concatenate to strings which are
being print()-ed. This uses the decode() method to turn them from bytes
objects into string objects, assuming they represent UTF-8. In python
2, bytes objects and strings are treated interchangeably, and so this
isn't necessary.

Change-Id: Ifc5d788e1c62751090a350d3a064e89f434559e8
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23265
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>