Fix AppendEntry logic when prevLogIndex and prevLogTerm is -1

Fix AppendEntry logic when prevLogIndex and prevLogTerm is -1

When an AppendEntry arrives at a Follower with the prevLogIndex and
prevLogTerm = -1 the Follower will accept that append entry and add it
to the log. For a newly started Follower this can be problematic
because this will be the first entry in that Followers log and so
applying this entry to the Follower's state can end up corrupting the
state or cause failures in committing transactions.

To fix this we now verify if the replicatedToAllIndex is present in the
Followers log. If it is present then the log is considered in sync else
not.

Change-Id: I09bead430f1a4556182263de54846792668cd27c
Signed-off-by: Moiz Raja <moraja@cisco.com>