LCP IP allocation algorithm - try harder to find a candidate source node

LCP IP allocation algorithm - try harder to find a candidate source node

There's a bug in LCP2.  Selecting the node with the highest imbalance
doesn't always work.  Some nodes can have a high imbalance metric
because they have a lot of IPs.  However, these nodes can be part of a
group that is perfectly balanced.  Nodes in another group with less
IPs might actually be imbalanced.

Instead of just trying the source node with the highest imbalance this
tries them in descending order of imbalance until it finds one where
an IP can be moved to another node.

Signed-off-by: Martin Schwenke <martin@meltin.net>