mongodb replica set support

Use the configure_replicaset library method from the
edelight/chef-mongodb repository by Markus Korn.
use the arbiter node attribute when configuring replica sets
handle mongodb replica sets with an even number of members

We use a different role for installing the mongodb service when HA is
enabled. That way we can decide which nodes get to have mongodb in the
barclamp code and we can enforce an odd number of nodes.
remove unused replica_set arbiter setting