Have LDAP return a better error message if it fails to connect

Currently, the error results in a 500 being raised when a user tries to login.

test/test_ldap.py

@@ -85,6 +85,24 @@ class TestLDAP(unittest.TestCase):
     finished_database_for_testing(self)
     self.ctx.__exit__(True, None, None)
 
+  def test_invalid_admin_password(self):
+    base_dn = ['dc=quay', 'dc=io']
+    admin_dn = 'uid=testy,ou=employees,dc=quay,dc=io'
+    admin_passwd = 'INVALIDPASSWORD'
+    user_rdn = ['ou=employees']
+    uid_attr = 'uid'
+    email_attr = 'mail'
+
+    ldap = LDAPUsers('ldap://localhost', base_dn, admin_dn, admin_passwd, user_rdn,
+                     uid_attr, email_attr)
+
+    self.ldap = ldap
+
+    # Try to login.
+    (response, err_msg) = self.ldap.verify_user('someuser', 'somepass')
+    self.assertIsNone(response)
+    self.assertEquals('LDAP Admin dn or password is invalid', err_msg)
+
   def test_login(self):
     # Verify we can login.
     (response, _) = self.ldap.verify_user('someuser', 'somepass')