Jialei gh270 connect cuda ei to optimization algorithm

********* PEOPLE *************
Primary reviewer: @suntzu86

Reviewers: @sc932

********* DESCRIPTION **************
Branch Name: jialei_gh270_connect_cudaEI_to_optimization_algorithm
Ticket(s)/Issue(s): Closes #270 

********* TESTING DONE *************
make test
cpplint.py
instead of "1" and "0", i'd create or use explicit variables with these values so that the reader immediately knows what they mean

also i believe you can pass nullptr in place of ```&dummy_rng```.