BUG 2817 - Create reusable classes for doing an action on finding primary

BUG 2817 - Create reusable classes for doing an action on finding primary

For AddShardReplica we are finding the primary and when it is found we send
a ForwardedAddServer* message to self. I need to do something similar for
RemoveShardReplica - so I've extracted the design pattern that was used for
AddShardReplica into a set of reusable classes. To start with this I can
use this for RemoveShardReplica but I think it can be used for other such
messages in future.

Change-Id: Ib625403f6eab5b07bc126af9db3d4e6e566e2038
Signed-off-by: Moiz Raja <moraja@cisco.com>