(TWILL-85) Make ZK-coordinated leader election available to twill applications
Bump version to 0.4.0-incubating-SNAPSHOT
Merge remote-tracking branch 'upstream/master'
Review Comments. Removed getNode() from ContainerInfo classes. Changed Hosts and Racks classes to have Set instead of List. Refactored Blacklist code into method manageBlacklist. Removed unused imports, extra blank lines. Fixed empty javadocs and split-line indentations. Other review comments.