Pulled out mvndst parameters

********* PEOPLE *************
Primary reviewer: @sc932 

Reviewers: @suntzu86 

********* DESCRIPTION **************
Branch Name: denizokt_376_fixflakes
Ticket(s)/Issue(s): Closes #376 

********* TESTING DONE *************
make test
make style-test
made sure demos and pretty endpoints still work
i'd reference:
http://www.math.wsu.edu/faculty/genz/software/fort77/mvndstpack.f

here too--for more info about the parameters