Fix ShardTest#testCreateSnapshot unit test failures

Fix ShardTest#testCreateSnapshot unit test failures

This unit test is failing on jenkins quite often due to a timing issue
with the tests resulting from recent changes. Basically akka uses a
calling thread dispatcher by default so the call to
createSnapshotProcedure in the SnapshotManager may result in a direct
call to persist which fails b/c it's still in the Idle state. Moving the
setting of currentState to CREATING prior to calling
createSnapshotProcedure fixes the issue.

Change-Id: If68333d042896e25fd3f85dd16da7b84ca56d944
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>