Disable R0922 in pylint

R0922, “Abstract class is only referenced 1 times”, cannot be disabled
in the source code, and thus
lib/http/auth.py:HttpServerRequestAuthentication gives this warning
(it's actually also referenced from the tests, but we do not include
them).

Therefore we need to disable it at pylintrc level.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Olivier Tharan <olive@google.com>

pylintrc

@@ -105,4 +105,4 @@ disable-msg-cat=
 #enable-msg=
 
 # Disable the message(s) with the given id(s).
-disable-msg=W0511
+disable-msg=W0511,R0922