Combine batches of successive roles for same nodes,

we can speed-up the application of (n+1)th role if the n if both the
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

@@ -1071,6 +1071,8 @@ def apply_role(role, inst, in_queue, bootstrap = false)
 
     # element_order is an Array where each item represents a batch of roles and
     # the batches must be applied sequentially in this order.
+    pnodes_in_batch = nil
+    proles = nil
     element_order.each do |roles|
       # roles is an Array of names of Chef roles which can all be
       # applied in parallel.
@@ -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 pnodes_in_batch == nodes_in_batch && !proles.nil?
+        # proles is same as batches[-1][0]
+        proles << roles
+      else
+        proles = roles
+        pnodes_in_batch = nodes_in_batch
+        batches << [roles, nodes_in_batch] unless nodes_in_batch.empty?
+      end
     end
     Rails.logger.debug "batches: #{batches.inspect}"