CLOUDIFY-1535 Candidate node refactoring.

- Trigger leader election on cluster members list change instead of startup.
CLOUDIFY-1535 Changed candidate node lifecycle methods to start & stop

- Implementations should override the doStart() and doStop() methods for extra functionality.
CLOUDIFY-1535 call out-of-sync event when moved to read-only mode

- Removed unused abstract methods.
- Updated javadoc.
CLOUDIFY-1535 Changed leader projects to use cosmo-logger.
CLOUDIFY-1535 Changed leader projects to use cosmo-logger.

- Added a scheduled logging mechanism for logging leader election status if no election was made.
- Added log messages enums & properties files.
CLOUDIFY-1535 Switched to FEST assertions from hamcrest.
CLOUDIFY-1535 Updated Guava dependency to version 14.0.