fix forward port of #46751

self.opts key 'environment' have been renamed to 'saltenv' after 2017.7,
thus the forward port broke the 'same' merging strategy again.

salt/state.py

@@ -2999,7 +2999,7 @@ def get_tops(self):
                     'top_file_merging_strategy set to \'same\', but no '
                     'default_top configuration option was set'
                 )
-            self.opts['environment'] = self.opts['default_top']
+            self.opts['saltenv'] = self.opts['default_top']
 
         if self.opts['saltenv']:
             contents = self.client.cache_file(