CDS: ShardManagerTest cleanup

Added a Builder to TestShardManager and modified tests to use the
Builder to gain more consistency between the tests. As a result, I made the
ShardManager builder class abstract for derivation same as was done for
the Shard builder.

I removed the ForwardingShardManager class and merged the functionality
into TestShardManager.

Change-Id: I55471b388a40b9da68bdb249f4cc597d2a0e7f90
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>