tempest/test.py: make set_validation_resources() more idiomatic

It's a cosmetic change but it shouldn't be controversial.

Change-Id: Ia02844319565eebea92ed8b0628dea37bdd22063
diff --git a/tempest/test.py b/tempest/test.py
index 93fbed3..be2e6e1 100644
--- a/tempest/test.py
+++ b/tempest/test.py
@@ -532,18 +532,17 @@
         """
         if not CONF.validation.run_validation:
             return
+
         if keypair is None:
-            if CONF.validation.auth_method.lower() == "keypair":
-                keypair = True
-            else:
-                keypair = False
+            keypair = (CONF.validation.auth_method.lower() == "keypair")
+
         if floating_ip is None:
-            if CONF.validation.connect_method.lower() == "floating":
-                floating_ip = True
-            else:
-                floating_ip = False
+            floating_ip = (CONF.validation.connect_method.lower() ==
+                           "floating")
+
         if security_group is None:
             security_group = CONF.validation.security_group
+
         if security_group_rules is None:
             security_group_rules = CONF.validation.security_group_rules