Add a basic help option and usage description which is consistent
with arcstat.py and dbufstat.py. This also adds support for long
opts.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Kyle Blatter <kyleblatter@llnl.gov>
Signed-off-by: Ned Bass <bass6@llnl.gov>