Merge branch 'reduce_parallel_sns' into 'v2015.1.2'

Reduce parallel connections to supernodes

Reduce the number of supernodes a node connects to. This is done in order
to reduce the amount of broadcast traffic sent to clients. Currently
a supernode sends about 3MiB/s broadcast traffic to clients. Reducing
the number of nodes will hopefully also reduce the amount of broadcast
traffic on supernodes.

See merge request !13