Mail notification - encoding exception not catched

[mohierf]

When message content is UTF-8 encoded an uncatched exception is raised and the mail notification is not sent. As an example:

./notify_by_email.py -n service -S localhost -r test@localhost -f html -c "PROBLEM,,localhost,,127.0.0.1,,Mon 02 Nov 11:20:09 UTC 2015" -o "Services,,CRITICAL,,CRITICAL - 'Frédéric',,48h 05m 58s"

Traceback (most recent call last):
  File "/var/lib/shinken/libexec/notify_by_email.py", line 370, in <module>
    mail = create_html_message(mail)
  File "/var/lib/shinken/libexec/notify_by_email.py", line 228, in create_html_message
    html_msg = html_content.encode(sys.stdout.encoding)
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 1783: ordinal not in range(128)