benchmarking invocation performance

usage: ./invoker_socket_clean.py num_connections num_threads

Results from a EC2 node

python invoker_socket_clean.py 5000 1
num connections: 5000 threads: 1
connection: 26.853372097
sent: 0.0873599052429
recv: 11.457463026

python invoker_socket_clean.py 5000 10
num connections: 5000 threads: 10
connection: 4.61677002907
sent: 0.133472919464
recv: 10.0993602276

python invoker_socket_clean.py 10000 20
num connections: 10000 threads: 20
connection: 8.43912696838
sent: 0.146968126297
recv: 11.8716299534