Support for alias interfaces

I'm testing TripleO on some temporary nodes, until my real hardware arrives.

There is currently only one NIC available on each node, so I've created alias interfaces.

It looks like os-net-config does not support these, because it makes a simple search for /sys/class/net/<interface name> rather than the parent interface name.

E.g.

 "[2018/04/13 11:16:02 AM] [INFO] Using config file at: /etc/os-net-config/config.json",
                "[2018/04/13 11:16:02 AM] [INFO] Ifcfg net config provider created.",
                "[2018/04/13 11:16:02 AM] [INFO] Not using any mapping file.",
                "[2018/04/13 11:16:03 AM] [INFO] Finding active nics",
                "[2018/04/13 11:16:03 AM] [INFO] lo is not an active nic",
                "[2018/04/13 11:16:03 AM] [INFO] em1 is an embedded active nic",
                "[2018/04/13 11:16:03 AM] [INFO] docker0 is not an active nic",
                "[2018/04/13 11:16:03 AM] [INFO] No DPDK mapping available in path (/var/lib/os-net-config/dpdk_mapping.yaml)",
                "[2018/04/13 11:16:03 AM] [INFO] Active nics are ['em1']",
                "[2018/04/13 11:16:03 AM] [INFO] nic1 mapped to: em1",
                "[2018/04/13 11:16:03 AM] [INFO] adding bridge: br-ctlplane",
                "[2018/04/13 11:16:03 AM] [ERROR] Unable to read mac address: em1:1",

where I have used parameter_defaults in the undercloud deploy command invocation to set the interface name to em1:1