{Process, Cluster}Task use single string commands.

[nicmcd]

Subprocess ideally wants to receive subprocess commands as lists of strings:
https://docs.python.org/3/library/subprocess.html#frequently-used-arguments

"Providing a sequence of arguments is generally preferred, as it allows the module to take care of any required escaping and quoting of arguments (e.g. to permit spaces in file names)."

The direction is to change to list of strings. This changes the API of taskrun, but for the better.