Bug-2301 - Clustering:Snapshots need not be stored in in-mem ReplicatedLog for Installing snapshots

1. Snapshots, once persisted to disk, would not be stored as part of ReplicatedLog in memory
2. An Install snapshot would initiate a snapshot capture and be sent to the follower
3. FollowerLogInformation in Leader has a stopwatch which helps to find if a given follower is active/up.

Rebased

Change-Id: If7aac2518a0f624a0cc121112ce165456d002a18
Signed-off-by: Kamal Rameshan <kramesha@cisco.com>
(cherry picked from commit 2b0c99463883b10d5eacdec901d7543d5815a54f)
Merge "Bug-2301 - Clustering:Snapshots need not be stored in in-mem ReplicatedLog for Installing snapshots" into stable/helium