Where did you get that meaning of 'luck'? Turkish name websites like
http://www.bebek.com/ do not list a name of Mirvat or Mervat, and Turkish dictionaries know nothing about such a word meaning luck, as far as I could see.
I also found the following piece of info:
http://en.allexperts.com/q/Turkish-Language-3389/2008/8/Language.htm
Rene
www.BabyNames.ch