Remove duplicate negative test of flavor_id

As tempest/api/compute/admin/test_flavors.py, it is possible to
specify uuid as flavor_id. In addition, Nova creates a flavor with
uuid flavor_id if passing None as the API parameter of flavor_id.

Then, test_get_flavor_details_for_invalid_flavor_id is not an
"invalid id" test, the test is a "non existent id" test.
So the test and test_non_existent_flavor_id are duplicated, and
this patch merges them to one test.

Change-Id: I73f79f82f48a49208500c2542e55c026f120e921
diff --git a/tempest/api/compute/flavors/test_flavors_negative.py b/tempest/api/compute/flavors/test_flavors_negative.py
index 81e4f87..0b20e90 100644
--- a/tempest/api/compute/flavors/test_flavors_negative.py
+++ b/tempest/api/compute/flavors/test_flavors_negative.py
@@ -18,7 +18,6 @@
 import uuid
 
 from tempest.api.compute import base
-from tempest.common.utils import data_utils
 from tempest import exceptions
 from tempest.test import attr
 
@@ -31,14 +30,6 @@
         super(FlavorsNegativeTestJSON, cls).setUpClass()
         cls.client = cls.flavors_client
 
-        # Generating a nonexistent flavor id
-        resp, flavors = cls.client.list_flavors()
-        flavor_ids = [flavor['id'] for flavor in flavors]
-        while True:
-            cls.nonexistent_flavor_id = data_utils.rand_int_id(start=999)
-            if cls.nonexistent_flavor_id not in flavor_ids:
-                break
-
     @attr(type=['negative', 'gate'])
     def test_invalid_minRam_filter(self):
         self.assertRaises(exceptions.BadRequest,
@@ -52,17 +43,11 @@
                           {'minDisk': 'invalid'})
 
     @attr(type=['negative', 'gate'])
-    def test_get_flavor_details_for_invalid_flavor_id(self):
-        # Ensure 404 returned for invalid flavor ID
-        invalid_flavor_id = str(uuid.uuid4())
-        self.assertRaises(exceptions.NotFound, self.client.get_flavor_details,
-                          invalid_flavor_id)
-
-    @attr(type=['negative', 'gate'])
     def test_non_existent_flavor_id(self):
         # flavor details are not returned for non-existent flavors
+        nonexistent_flavor_id = str(uuid.uuid4())
         self.assertRaises(exceptions.NotFound, self.client.get_flavor_details,
-                          self.nonexistent_flavor_id)
+                          nonexistent_flavor_id)
 
 
 class FlavorsNegativeTestXML(FlavorsNegativeTestJSON):