Misleading log message when a node has a MAC address not attached to a cluster interface

[Jason Hobbs]

When a node has two nics, and one isn't attached to a cluster interface, this error is reproted in maas.log:

[ERROR] horrible-hour.local: Tried to allocate an IP to MAC 74:d4:35:89:bd:2f but its cluster interface is not known

In fact, there was no attempt to allocate an IP to the MAC . The log message is generated from MACAddress.get_cluster_interfaces(), which is used in map_gateways() during preseed generation.

If this needs to be logged, it should be moved to the caller that uses get_cluster_interfaces() when allocating IPs.

This is r3254.