[Docs] Fix doc building idempotency

When running the doc building a new scenario was generated,
and appened to the scenario-table-gen.html page. We should instead
generate that page from scratch, and ensure it's always the
same content. This doesn't clean the scenario table gen, it simply
makes sure the generated content is always ordered the same way.

Change-Id: I9098f5d76b73be5ef28684027ff5039cd52d6ddb

doc/source/conf.py

@@ -35,7 +35,7 @@ stg = imp.load_source(
     'scenario_table_gen',
     os.path.join(CONF_PATH, 'scenario_table_gen.py')
 )
-with open(TABLE_FILE, 'a+') as f:
+with open(TABLE_FILE, 'w') as f:
     f.write(stg.main())
 
 # If extensions (or modules to document with autodoc) are in another directory,

doc/source/scenario_table_gen.py

@@ -41,7 +41,7 @@ def main():
     for items in scenario_meta_data.values():
         for item in items:
             config_items.add(item['name'].split('.')[0])
-    config_items = list(config_items)
+    config_items = list(sorted(config_items))
 
     for item in config_items:
         HTML_TABLE += '<tr>'