raft: infrastructire for raft integration test

[SUMUKHA-PK]

To setup a thorough raft integration test we need the following up:

• A generic integration testing framework that uses actual multiple servers. (raft: create generic testing framework  #175 )
• A module to enable failing a server. (raft: module on the raft testing framework to kill servers #176)

General thoughts:

The test must run until the user determines and must allow the servers to crash and recover gracefully whilst the cluster runs raft.