Use args in build, manage flushCall bug

[bat52]

command_args argument exist but is not used. I found it useful to specify verilator arguments such as
args = ["-Wno-TIMESCALEMOD", "-Wno-WIDTH", '--timescale-override', '1ns/1ns'] as you can see here https://github.com/bat52/cryptech/blob/master/pycryptech/ecdsa256_pyverilator.py