Unuse resources after every test

Fix bug in put_all(). That method was unused before this commit.

Clean the process list after the processes are stopped,
otherwise the suite eventually fails with a 'process terminated
prematurely' error. Before it was not necessary because it was not
reused (a new suite run was created).

Change-Id: Iee12866045145544076c6c18786e1a54f18fc293
diff --git a/src/osmo_gsm_tester/resource.py b/src/osmo_gsm_tester/resource.py
index dbfc4e0..8eec71e 100644
--- a/src/osmo_gsm_tester/resource.py
+++ b/src/osmo_gsm_tester/resource.py
@@ -508,11 +508,11 @@
                     my_item.pop(USED_KEY)
 
     def put_all(self):
+        if not self.reserved:
+            return
         for key, item_list in self.reserved.items():
-            my_list = self.get(key)
-            for my_item in my_list:
-                if my_item.get(USED_KEY):
-                    my_item.pop(USED_KEY)
+            for item in item_list:
+                item.pop(USED_KEY, None)
 
     def free(self):
         if self.reserved: