rest: return input files and parameters in spec

closes reanahub#226
closes reanahub#227

reana_server/utils.py

@@ -290,8 +290,15 @@ def clone_workflow(workflow, reana_spec):
 
 def reconstruct_reana_yaml(workflow):
     """Reconstruct the REANA.yaml from a workflow object."""
-    return {
+    input_files = workflow.reana_specification.get('inputs', {}) \
+        .get('files', {})
+
+    spec = {
         'workflow': {
             'specification': workflow.get_specification(),
             'type': workflow.type_},
         'inputs': {'parameters': workflow.get_input_parameters()}}
+
+    if input_files:
+        spec['inputs']['files'] = input_files
+    return {'specification': spec, 'parameters': workflow.input_parameters}