get_user behavior in ldapdriver

* Addresses bug 744462

Rather than ldapdriver.get_user() returning None for non-existent
user, this change implements exception.LDAPUserNotFound to more
closely match the behavior of other drivers (db).

Change was made in public method only, and _check_user_exists()
which uses get_user() now catches and returns None if applicable.
Implemented test of NotFound exception in base auth test class.

Change-Id: Ia13af759931ca0c7327d54184730537bafbe52ae

nova/auth/ldapdriver.py

@@ -223,6 +223,8 @@ def inner(self, arg, **kwargs):
     def get_user(self, uid):
         """Retrieve user by id"""
         attr = self.__get_ldap_user(uid)
+        if attr is None:
+            raise exception.LDAPUserNotFound(user_id=uid)
         return self.__to_user(attr)
 
     @sanitize
@@ -495,7 +497,10 @@ def modify_user(self, uid, access_key=None, secret_key=None, admin=None):
 
     def __user_exists(self, uid):
         """Check if user exists"""
-        return self.get_user(uid) is not None
+        try:
+            return self.get_user(uid) is not None
+        except exception.LDAPUserNotFound:
+            return False
 
     def __ldap_user_exists(self, uid):
         """Check if the user exists in ldap"""

nova/tests/test_auth.py

@@ -394,6 +394,11 @@ def test_can_call_modify_user_but_do_nothing(self):
             self.assertEqual(old_user.secret, user.secret)
             self.assertEqual(old_user.is_admin(), user.is_admin())
 
+    def test_get_nonexistent_user_raises_notfound_exception(self):
+        self.assertRaises(exception.NotFound,
+                          self.manager.get_user,
+                          'joeblow')
+
 
 class AuthManagerLdapTestCase(_AuthManagerBaseTestCase):
     auth_driver = 'nova.auth.ldapdriver.FakeLdapDriver'