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
the original defaults were like 1.0e-6 and 20,000. any reason for the change?

also, the default values and the suggested values in the docstring don't match?