Having a file with the same name as its package creates hard-to-diagnose
import error, so rename mininet.py to net.py. This commit moves utility
functions, generally those dealing with network namespaces and interface
management, into their own file.
Also fix a few minor formatting bugs and clean up logging code (which
had issues when multiple files would import mininet.logging_mod).
Brandon Heller
220890a0c9