Fix H404/405 violations for common code

There is a lot of H404/405 violations in Tempest now, and that leads
difficult to migrate the code to tempest-lib or the other projects'
repos. This patch fixes these violations for common code.

Change-Id: I5ddedcdd4d00ddbd53e1006ba40dce447fba3c20
diff --git a/tempest/common/credentials_factory.py b/tempest/common/credentials_factory.py
index 486b7fd..75639b2 100644
--- a/tempest/common/credentials_factory.py
+++ b/tempest/common/credentials_factory.py
@@ -292,10 +292,7 @@
 
 
 class ConfiguredUserManager(clients.Manager):
-    """
-    Manager object that uses the `user` credentials for its
-    managed client objects
-    """
+    """Manager that uses user credentials for its managed client objects"""
 
     def __init__(self, service=None):
         super(ConfiguredUserManager, self).__init__(
@@ -304,11 +301,7 @@
 
 
 class AdminManager(clients.Manager):
-
-    """
-    Manager object that uses the admin credentials for its
-    managed client objects
-    """
+    """Manager that uses admin credentials for its managed client objects"""
 
     def __init__(self, service=None):
         super(AdminManager, self).__init__(