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
note that this code is copypasted & from where