Move assign_keypair method in base class

Change-Id: I69b8db037991f88b38b293560532bf51c0a04378
diff --git a/scenario/test_server_cfn_init.py b/scenario/test_server_cfn_init.py
index 9d85120..a98747c 100644
--- a/scenario/test_server_cfn_init.py
+++ b/scenario/test_server_cfn_init.py
@@ -25,18 +25,11 @@
         super(CfnInitIntegrationTest, self).setUp()
         if not self.conf.image_ref:
             raise self.skipException("No image configured to test")
+        self.assign_keypair()
         self.client = self.orchestration_client
         self.template_name = 'test_server_cfn_init.yaml'
         self.sub_dir = 'templates'
 
-    def assign_keypair(self):
-        if self.conf.keypair_name:
-            self.keypair = None
-            self.keypair_name = self.conf.keypair_name
-        else:
-            self.keypair = self.create_keypair()
-            self.keypair_name = self.keypair.id
-
     def launch_stack(self):
         net = self._get_default_network()
         parameters = {
@@ -114,6 +107,5 @@
                 raise e
 
     def test_server_cfn_init(self):
-        self.assign_keypair()
         sid = self.launch_stack()
         self.check_stack(sid)