Update Elixir tests for using new auth API

test/ejabberd_auth_mock.exs

@@ -32,7 +32,7 @@ defmodule EjabberdAuthMock do
 
 		{:ok, _pid} = Agent.start_link(fn -> %{} end, name: @agent)
 
-		mock(:ejabberd_auth, :is_user_exists,
+		mock(:ejabberd_auth, :user_exists,
 			fn (user, domain)  ->
 				Agent.get(@agent, fn users -> Map.get(users, {user, domain}) end) != nil
 			end)

test/ejabberd_cyrsasl_test.exs

@@ -114,7 +114,7 @@ defmodule EjabberdCyrsaslTest do
       fn (_host) ->
         true
       end)
-    mock(:ejabberd_auth, :is_user_exists,
+    mock(:ejabberd_auth, :user_exists,
       fn (user, domain) ->
         domain == "domain1" and get_password(user) != {:false, :internal}
       end)