impala-shell is slow with hs2-http

The following command takes 1.5 sec with hs2 and 8.5 sec with hs2-http ptotocol on my dev machine:

shell/impala_shell.py -B -q "select * from tpch_parquet.lineitem limit 100000;" --protocol hs2-http > /dev/null

Profiling has shown that the main culprit is calling socket.recv() 2809090 times. The root cause is the lack of buffering in our current http client implementation.