Adds message prefix to chef handler
Adds message prefix to chef handler

Adds an option to prefix a string before the message, such as for an
@all mention.

scalixte-mdsol/hipchat-rb,hipchat/hipchat-rb,hipchat/hipchat-rb,bonusly/hipchat-rb,bonusly/hipchat-rb,StatusPage/hipchat-rb,banrui/hipchat-rb,ph/hipchat-rb