Adds modules for managing network interfaces for generic driver

Adds modules for creating and managing
logical interfaces. This modules create logical
interface and attach it to OVS or Linux bridge
to associate with neutron port.
Module manila.network.linux.ip_lib.py executes
linux 'ip' command for logical interface setup.
Module manila.network.linux.interface.py
is responsible for plugging logical interface
into OVS or Linux bridge.
Class in module manila.network.linux.ovs_lib.py
represents OVS bridge and allows to manage it.

Partially implements: bp generic-driver
Change-Id: Iaa97e961f1670479a59a2f9adba5953d271b1818