rabbitmq: adjust things to avoid messy partitions

We have been having the cluster fall over for still unknown reasons,
but this patch should at least help prevent them:

first we increase the net_ticktime parameter from it's default of 60 to 120.
rabbitmq sends 4 'ticks' to other cluster members over this time and if 25%
of them are lost it assumes that cluster member is down. All these vm's are
on the same net and in the same datacenter, but perhaps heavy load
from other vm's causes them to sometimes not get a tick in time?
http://www.rabbitmq.com/nettick.html

Also, set our partitioning strategy to autoheal. Currently if some cluster
member gets booted out, it gets paused, and stops processing at all.
With autoheal it will try and figure out a 'winning' partition and restart
all the nodes that are not in that partition.
https://www.rabbitmq.com/partitions.html

Hopefully the first thing will make partitions less likely and the second
will make them repair without causing massive pain to the cluster.

Signed-off-by: Kevin Fenzi <kevin@scrye.com>

roles/rabbitmq_cluster/templates/rabbitmq.config

@@ -21,7 +21,7 @@
 
    %% How to respond to cluster partitions.
    %% Documentation: https://www.rabbitmq.com/partitions.html
-   {cluster_partition_handling, pause_minority},
+   {cluster_partition_handling, autoheal},
 
    %% And some general config
    {log_levels, [{connection, none}]},
@@ -29,9 +29,7 @@
    {heartbeat, 600},
    {channel_max, 128}
   ]},
- {kernel,
-  [
-  ]},
+ {kernel, [{net_ticktime,  120}]},
  {rabbitmq_management,
   [
    {listener, [{port, 15672},