do not try to stop server if it has been already stopped

Author: zilder

setup.py

@@ -2,7 +2,7 @@
 setup(
   name = 'testgres',
   packages = ['testgres'],
-  version = '0.1.5',
+  version = '0.1.6',
   description = 'Testing utility for postgresql and it''s extensions',
   author = 'Ildar Musin',
   author_email = 'zildermann@gmail.com',

testgres/testgres.py

@@ -372,4 +372,6 @@ def clean_all():
 def stop_all():
     global registered_nodes
     for node in registered_nodes:
-        node.stop()
+        # stop server if it still working
+        if self.working:
+            node.stop()