nfs-utils: nfs-iostat.py autofs cleanup and option to sort by ops/s

Here's the reworked patchset for nfs-iostat.py, separating out:
* the python path change
* the version bump due to adding a feature
* the autofs mountpoint add/drop rescanning
* the --sort and -<n> features

Thanks again for considering this.

-- Lans Carstensen, Systems Engineering, Dreamworks Animation Because they consistently observe and listen, the humble improve.
-- Wynton Marsalis