Clean up formatting in PKB file - working on aerospike_benchmark.py file

[ishita2411]

Hello
I am working on the this issue in aerospike_benchmark.py file

Goal to convert
flags.DEFINE_integer(
'aerospike_client_threads_step_size',.....)

to

AEROSPIKE_CLIENT_THREAD_STEP_SIZE = flags.DEFINE_integer(
'aerospike_client_threads_step_size',.....)

and change its uses accordingly