Do not import anything from quantum into rootwrap

The rootwrapper is special and shouldn't do heavy code
loading, first for performance and 2nd for potential
security issues.

It shaves off 0.2s of load time (aka heavy cpu usage when
using openvswitch as it invokes rootwrap twice every 4 seconds)

Fixes LP bug 1190675

This is reverting bug 1053381

    Author: Gary Kotton <gkotton@redhat.com>
    Date:   Sun Sep 23 08:34:33 2012 +0000

        Uses a common subprocess popen function

Change-Id: I629d90aaeb99b225d716da82c6ac5c3f327ebb67
Merge "Do not import anything from quantum into rootwrap" into stable/grizzly