Bug 4149: Implement per-shard DatastoreContext settings

Bug 4149: Implement per-shard DatastoreContext settings

Added the ability to specify shard-specific settings in the .cfg file by
prefixing the shard name to the property name, similar to what we allow
at the datastore level.

I added a DatastoreContextFactory that has methods to get the base
DatastoreContext and a per-shard DatastoreContext. The
DatastoreContextFactory is now passed to the ShardManager instead of the
DatastoreContext. The DatastoreContextFactory uses the
DatastoreContextIntrospector to overlay per-shard settings onto the
base DatastoreContext.

Change-Id: I329c98c1577a74ebe665052f76e28da3867e2e86
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>