erasure-code: separate profile from pool creation

So, the reason I kept suggesting using proper arguments was that I don't like when defaults are obscured unnecessarily in source code (as opposed to the function signature, which is accessible via things like documentation generators and ```help()```).

Adding comments like the one you added is helpful, but for the same reason as I mentioned above, not as helpful as a docstring:
http://legacy.python.org/dev/peps/pep-0257/