Combine batches of successive roles for same nodes,

we can speed-up the application of (n+1)th role if both(n,n+1)
roles are being applied on the same node. This speedup of deployment of
ceilometer by atleast 1m20s (measured: 90sec) and swift by ~20s.

eg. In our 2node deployment ceilometer{server,central} are always
applied on the same node, given that they have different priorities, they are
to be applied, one after the other.

This does not violate any order constraints as the application procedure
of (n+1)th role is transparent to the nth role

crowbar_framework/app/models/service_object.rb

@@ -1069,6 +1069,8 @@ def apply_role(role, inst, in_queue, bootstrap = false)
     proposal = Proposal.where(barclamp: @bc_name, name: inst).first
     save_proposal = false
 
+    nodes_previousbatch = nil
+    roles_previousbatch = nil
     # element_order is an Array where each item represents a batch of roles and
     # the batches must be applied sequentially in this order.
     element_order.each do |roles|
@@ -1169,7 +1171,14 @@ def apply_role(role, inst, in_queue, bootstrap = false)
         end
       end # roles.each
 
-      batches << [roles, nodes_in_batch] unless nodes_in_batch.empty?
+      if nodes_previousbatch == nodes_in_batch && !roles_previousbatch.nil?
+        # roles_previousbatch is same as batches[-1][0]
+        roles_previousbatch << roles
+      else
+        roles_previousbatch = roles
+        nodes_previousbatch = nodes_in_batch
+        batches << [roles, nodes_in_batch] unless nodes_in_batch.empty?
+      end
     end
     Rails.logger.debug "batches: #{batches.inspect}"