Add VIF mac address to fixed_ips in notifications

Currently the payload of the notification only contains fixed_ips from VIFs,
the mac address from VIFs is also a very important information and
should be included with the payload of the notification.

This patch add the VIF mac address to each fixed_ips as a new attribute
named "vif_mac".
Notification will looks like:
 	u'fixed_ips': [{u'address': u'192.168.44.1',
                           u'floating_ips': [],
                           u'label': u'publica',
                           u'meta': {},
                           u'type': u'fixed',
                           u'version': 4,
                           u'vif_mac': u'fa:16:3e:93:ec:d5'}],

Closes-Bug: #1320374
Change-Id: I071b8fa75fecdae556c7ad72878ca8f86cf57139
Merge "Add VIF mac address to fixed_ips in notifications"