An attempt at fixing some encoding issues

This patch unifies the hardcoded re-encoding attempts into a single
function in utils.py. This function is used to take either an unicode or
str object and convert it to a ASCII-only str object which can be safely
displayed and transmitted.

We replace then the current manual re-encodings with this function. In
mcpu we stop re-encoding the hooks output and instead we do it right at
the hook generation in backend.py.

This passes on my 'custom' lvs output with non-ASCII chars. But there
are probably other places we will need to fix.

Reviewed-by: ultrotter