Bug 3020: Add version to AppendEntries and AppendEntriesReply

Bug 3020: Add version to AppendEntries and AppendEntriesReply

To handle backwards compatibility, a leader needs to know the version of
its followers wrt to the derived RaftActor's payload data. This will
enable
the derived RaftActor to translate its payload data to an older version.
So I added a version field to AppendEntriesReply which the leader stores
in the FollowerLogInformation.

In addition, a follower needs to know the version of its leader so we
can handle backwards compatibility wrt to transactions since we no
longer send the CreateTransaction message to the leader (currently only
for write-only). This patch adds a version field to AppendEntries - a
subsequent patch will utilize it.

Change-Id: I41632024a270206153e7c5d363ee1c79800e4200
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>