TAJO-704: TajoMaster HA

I implemented TajoMaster HA Manager utilizing HDFS Cluster. I defined a interface named HAManager, and I implemented HAManagerWithHDFS with the interface. 

To use TajoMaster HA, you have to set tajo.master.ha.enable=true at tajo-site.xml. And then, you just run standby master. All master informations will record to hdfs cluster, and all tajo service will refer master service address using hdfs cluster.

For reference, this patch includes a few issues as follows:

- It just implemented one unit test case because of TAJO-942. 
- If you kill current master and you already ran tsql, you have to restart tsql. because new master doesn't know existing session ids. We need to handle this issue at another ticket.

It would be better to use conf.setVar() instead of conf.set().