Added addditional logic to deterine if the hardware address for and inte...

Added logic to determine if the hardware address for an interface is 0x0 if so go to the next interface.

If someone was building from an image that already had something similar to openvpn installed where there was a tun* adapter created the nova-agent would segfault and all further processing would stop. This checks to see if the hardware address of the interface is 0x0, if so the it should continue to the next interface.

This should address issue https://github.com/rackerlabs/openstack-guest-agents-unix/issues/44