Speedup tests

There are lots of tests that were sleeping too long.
Other testing things that are not actually necessary (like Redis behavior... we can leave that for Redis tests :) ).
And I refactored sentinel tests to be more reliable and fast by using sentinel pubsub instead of doing a loop and sleeping.

Also I moved all the setup of master-slave to Makefile, so when the test runs, the context is already ready, and there is not need to configure everything there and wait for changes to happen