Bug 1577: Gates access to Shard actor until its initialized

1. Shard manager creates Shard and mark them un-initialized.
   Shard completes recovery and onRecoveryComplete, sends a
   message to Shard manager to mark it initialized.
   If a request for Shard comes to Shard manager and the
   shard is not initialized, it sends ActorNotInitialized
   message.

2. Normalizes and refactors ActorContext.

3. Adds AbstractUntypedPersistentActorWithMetering to meter
   ShardManager.

Change-Id: Ibf15a2ef56422bda53067039d2271a719b6b2ce3
Signed-off-by: Abhishek Kumar <abhishk2@cisco.com>