Remove unused directory.
Revert "Check style errors before running tests on Travis."

This reverts commit 4451de631d6471449508a6d9939ebe630540bd83.

We don't need a script to run scalastyle before test because 43f7d53ca5
makes test depend on scalastyle.
Create only one CuratorFramework.

CuratorFramework instances are fully threadsafe, so it is recommended to share
one CuratorFramework per ZooKeeper cluster.

Create CuratorSupervisor to manage the lifecycle of a CuratorFramework instance
and pass it to other actors upon creation.