Inital version of MultiReceive

This script will be the multithreaded version of the zfs receive test
Use the multiprocessing module

This makes the multithreading a little more clear
Use argparse for the output

We can have the -v flag determine if we want output on TXG and speed
status.
Get number of threads from the user

This allows the user to specify how many threads they want going at
once. Min of 1, max of 32
Remove SingleReceive

This is equivilent to MultiReceive -t 1, and this project already has
enough files in it.