client.shared.report: Set encoding to utf8 and allow customization.

When writing the HTML report, set the current encoding output to utf8.
Allow the customization of the encoding output too (with option -e)

It is know to work with LANG set en_US.utf8, pt_BR.utf8, fr_FR.utf8.

Fix issue #803.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
Merge pull request #804 from ruda/client_report_encoding

client.shared.report: Set encoding to utf8 and allow customization.