BUG 2185 : Disable all internal switching of behavior

BUG 2185 : Disable all internal switching of behavior

Since we do not depend on Raft for changing behavior when elections
are disabled we need to disable all internal switching of behaviors.

Added specific Leader tests to check the following,
1. Do not switch to Follower when you receive an AppendEntriesReply
   from a Follower with a higher term
2. Do not switch to IsolatedLeader even when no Follower is sending
   AppendEntriesReply

Change-Id: Ic2b4f76813f35db190e108306a62af5397d31658
Signed-off-by: Moiz Raja <moraja@cisco.com>
(cherry picked from commit 9baf6a2a5e494f70af407f04631980857a26daf9)