Use more specific asserts in tests

Instead of assertTrue and assertFalse use more specific asserts.
They are compatible with Python 2.7[1] and 3.4[2]

[1]: https://docs.python.org/2.7/library/unittest.html
[2]: https://docs.python.org/3.4/library/unittest.html

Change-Id: I3ac49863641e26841210d020e8bca0bd93176423
diff --git a/tempest/api/compute/keypairs/test_keypairs.py b/tempest/api/compute/keypairs/test_keypairs.py
index be6f615..562a508 100644
--- a/tempest/api/compute/keypairs/test_keypairs.py
+++ b/tempest/api/compute/keypairs/test_keypairs.py
@@ -57,8 +57,8 @@
         self.assertEqual(key_name, k_name,
                          "The created keypair name is not equal "
                          "to the requested name")
-        self.assertTrue(private_key is not None,
-                        "Field private_key is empty or not found.")
+        self.assertIsNotNone(private_key,
+                             "Field private_key is empty or not found.")
 
     @test.idempotent_id('a4233d5d-52d8-47cc-9a25-e1864527e3df')
     def test_get_keypair_detail(self):
@@ -72,8 +72,8 @@
                          "The created keypair name is not equal "
                          "to requested name")
         public_key = keypair_detail['public_key']
-        self.assertTrue(public_key is not None,
-                        "Field public_key is empty or not found.")
+        self.assertIsNotNone(public_key,
+                             "Field public_key is empty or not found.")
 
     @test.idempotent_id('39c90c6a-304a-49dd-95ec-2366129def05')
     def test_keypair_create_with_pub_key(self):
@@ -89,7 +89,7 @@
                    "XcPojYN56tI0OlrGqojbediJYD0rUsJu4weZpbn8vilb3JuDY+jws"
                    "snSA8wzBx3A/8y9Pp1B nova@ubuntu")
         keypair = self._create_keypair(k_name, pub_key)
-        self.assertFalse('private_key' in keypair,
+        self.assertNotIn('private_key', keypair,
                          "Field private_key is not empty!")
         key_name = keypair['name']
         self.assertEqual(key_name, k_name,