Introduce the ConfigureMemcg() method

The Service::Start() method is so long that its length negatively
affects readability of the code. Hence this patch that splits
Service::Start().

Test: Booted Android in Cuttlefish.
Change-Id: I972f4e60844bb0d133b1cca1fd4e06bb89fc5f37
Signed-off-by: Bart Van Assche <bvanassche@google.com>