cyclades: Add accounting for IP Addresses
Create IPAddressLog DB table to hold information about allocation of IP addresses to virtual servers. The information that is currently saved contains the IP address, the ID of the virtual server, the ID of the virtual network along with the datetime that the address has been allocated and released from the server. An entry in this table is created every time a NetworkInterface card that has an associated IP address is created in DB. The entry is updated with the 'released_at' timestamp when the NIC is destroyed in Ganeti. Currently, only IP addresses from public networks (network.public=True) are stored in this table. This commit also includes a DB data migration for all already allocated IP addresses. However, the 'allocated_at' timestamp of this entries will not be correct.