Commit 3154794d broke the HTML report
when older some versions of pystache is used.  The current status is
that the HTML report generated on those systems is a one line report
containing the literal `utf8` string.

This proposal does not try to add support Unicode based inputs with
that version of pystache, because it's internally not well supported.
Internal methods such as `Template.render_tags()` will blindly try to
do conversions without respecting the encoding passed on `render()`.

Also, it's true that we're missing Unicode support in many other
places, such as documented here in this card:

 https://trello.com/c/bfE9NBbl

For now, let's try properly generate the report, and keep the error
handling already present, that let's users know there have been
encoding errors.

References: https://trello.com/c/8j3aVUlISigned-off-by: NCleber Rosa <crosa@redhat.com>