Refactor configuration for ConfigPersister.

Pulled Configuration class from ConfigPusher that contains all the delays, timeouts and attempts numbers.

Add tests for config perister.

Change-Id: I187e721e0120931d0cca519353db840905816a20
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>
Merge "Refactor configuration for ConfigPersister."