crowbar: Fix Node.get_network_by_type for overridden attributes

We were looking for attributes overriding the network proposal only on
the node role, but this is not consistent with what the cookbook does
(it looks at attributes on the node itself), and customer using this
feature are more likely to edit the node directly.

So reflect that by looking at the node attributes, which does include
the attributes from the node role anyhow.

crowbar_framework/app/models/node.rb

@@ -647,11 +647,11 @@ def networks
 
   def get_network_by_type(type)
     return nil if @role.nil?
-    return nil unless crowbar["crowbar"]["network"].key?(type)
+    return nil unless @node["crowbar"]["network"].key?(type)
     # note that node might not be part of network proposal yet (for instance:
     # if discovered, and IP got allocated by user)
     return nil if @node["network"]["networks"].nil? || !@node["network"]["networks"].key?(type)
-    @node["network"]["networks"][type].to_hash.merge(crowbar["crowbar"]["network"][type].to_hash)
+    @node["network"]["networks"][type].to_hash.merge(@node["crowbar"]["network"][type].to_hash)
   end
 
   def set_network_attribute(network, attribute, value)