macspoof hooks: new hook script to enable macspoof filtering per vnic.

Puropose of this patch is to add a new hook script which is
almost equal to the existing one except that is applied on
a per vnic basis. This hook script uses a different custom
property ifacemacspoof to avoid conflicts with the macspoof
one which operates for all VM's interfaces.

* Patchset-1 first implmentation.
* Patchset-2 Removing for loop cycling through ifaces,
             the xml is only related to a specific iface.
* Patchset-3 Cherrypicked on top of fix broken storage test.
* Patchset-4 Changed custom property name from macspoofperdevice
             to ifacemacspoof, small fixes to README.
* Patchset-5 Updated implementation, fixed small issue
             related to the parsing code.
* Patchset-6 Updated README key is now part of CustomDeviceProperties.
* Patchset-7 Added before_nic_hotplug hook script.
* Patchset-8 Changed script name to macspoof_vnic and used it
             for 2 events instead of having two equal scripts.
             Updated Makefile and added docstring on top of the script.
* Patchset-9 Inlined removeFilter function, changed assignment 'style'.

Change-Id: Ifb3e7bec7ce400dddc6f4e649b7d21dfe5010631
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=908704
Signed-off-by: Giuseppe Vallarelli <gvallare@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/17678
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>