Fix NameError exception

The test_allocate_floating_ip can fail with "NameError:
name 'floating_ip_id_allocated' is not defined" if the
client.create_floating_ip call or response return fail.

Change-Id: I2db82ecf560c7d868ca9ab765a4fd751946b45f0
diff --git a/tempest/api/compute/floating_ips/test_floating_ips_actions.py b/tempest/api/compute/floating_ips/test_floating_ips_actions.py
index ff7188b..f1d5568 100644
--- a/tempest/api/compute/floating_ips/test_floating_ips_actions.py
+++ b/tempest/api/compute/floating_ips/test_floating_ips_actions.py
@@ -64,10 +64,10 @@
     def test_allocate_floating_ip(self):
         # Positive test:Allocation of a new floating IP to a project
         # should be successful
+        resp, body = self.client.create_floating_ip()
+        self.assertEqual(200, resp.status)
+        floating_ip_id_allocated = body['id']
         try:
-            resp, body = self.client.create_floating_ip()
-            self.assertEqual(200, resp.status)
-            floating_ip_id_allocated = body['id']
             resp, floating_ip_details = \
                 self.client.get_floating_ip_details(floating_ip_id_allocated)
             # Checking if the details of allocated IP is in list of floating IP