Separate Tajo's cluster resource manager from Yarn (Umbrella)

In the current implementation, the resource management of Tajo is tightly coupled to Hadoop Yarn. Hadoop YARN has emerged and a nice resource manager for large clusters, but Yarn is not the best choice for low latency query executions.

The main purpose of this issue is to separate Tajo's resource manager from Yarn and add a standby mode. In the standby mode, Tajo workers will be on standby, and they will provide low-latency responses for query tasks.

This issue is an umbrella issue, and our subtasks are as follows:

• We will separate QueryMaster from TajoMaster.
• We will provide a resource manager interface for Yarn and Tajo's one.
• We will implement our own resource manager and worker containers for the standby mode.

Finally, we will provide two modes:
(1) On-demand mode (using Yarn): in this mode, Tajo shares the cluster resource with another Yarn applications. Per query, Tajo will request necessary cluster resources.
(2) Standby mode: in this mode, Tajo master and workers will be on standby.