Add support to use current node parameters as references in class name

so that with the following reclass config:

```
=> /etc/reclass/nodes/mynode.yml
classes:
  - common
parameters:
  project: myproject

=> /etc/reclass/classes/common.yml
class:
  - ${project}

=> /etc/reclass/classes/myproject.yml
parameters:
  some:
    project: parameters
```

The mynode parameters would be merged successfully by reclass and we will
get the following result for the parameters:

```
parameters:
  project: myproject
  some:
    project: parameters
```

Without this patch, this would result in the following error:

```
Failed to load ext_pillar reclass: ext_pillar.reclass: -> mynode
	In yaml_fs:///etc/reclass/classes/common.yml
	Class name ${project} not resolvable
```
diff --git a/reclass/core.py b/reclass/core.py
index 61443c2..67b0f92 100644
--- a/reclass/core.py
+++ b/reclass/core.py
@@ -229,6 +229,7 @@
         base_entity.merge(self._get_class_mappings_entity(node_entity))
         base_entity.merge(self._get_input_data_entity())
         base_entity.merge_parameters(self._get_automatic_parameters(nodename, node_entity.environment))
+        base_entity.merge_parameters(Parameters(node_entity.parameters, self._settings, ''))
         seen = {}
         merge_base = self._recurse_entity(base_entity, seen=seen, nodename=nodename,
                                           environment=node_entity.environment)