macbind vdsm hook:
==================
This hook goes through all of the VM's interfaces and manipulate its
XML file acccording to the input. This can be used to attach a VM nic
to a specific bridge which is available in the hypervisor.

One specific use case being attach a virtual network interface to an
openvswitch bridge. Other being, attach  vm nic to a different bridge
than the defined/default bridge for that NIC.


Syntax:
    macbind={'mac': 'bridgename'}

Where:
    mac: specify the mac address of the vNIC to be attached to the bridge
    bridgename: Bridge Name available on hypervisor

Example:
    macbind={'00:1a:4a:41:d2:5f':'br0'}
    macbind={'00:1a:4a:41:d2:5f':'br0', '00:1a:4a:41:d2:60':'br1'}

Installation:
    - Use the engine-config to append the proper custom property:
        $ sudo engine-config -s \
        UserDefinedVMProperties='previousProperties;macbind=^.*$'
    - Verify that the macbind custom property was properly added:
        $ sudo engine-config -g UserDefinedVMProperties

Usage:
    In the VM configuration window, open the custom properites tab, select
    macbind and add proper value. i.e. {'00:1a:4a:41:d2:5f':'br0'}