Added RELAY_METHOD remove-node-consistent-hashing

This change adds a new relay method which determines the destination of the
metric by first removing a specified node from the metric. A case where this
is useful is when you want to aggregate metrics across all hosts, and the host
name is attached to the metric. This rule allows you to efficiently remove the host
name node without having to use any aggregation rules. It will then use
consistent hashing to group the same metrics to the same aggregator instance.

To use this relay method, add in the [relay] section:
#Removes first node of the metric
RELAY_METHOD = remove-node-consistent-hashing
REMOVE_NODE_INDEX = 0 

REMOVE_NODE_INDEX can have negative indices.