Bug 2948: Store DataPersistenceProvider in RaftActorContext

Bug 2948: Store DataPersistenceProvider in RaftActorContext

This will make the DataPersistenceProvider accessible to callers that
don't have access to the RaftActor. In particular, the SnapshotManager
will need access from the capture method (subsequent patch). The
DataPersistenceProvider can't be passed to capture b/c it is also
called from AbstractLeader which doesn't have access to the
DataPersistenceProvider.

With thus change we no longer have to pass the DataPersistenceProvider to
the persist and commit methods either.

Change-Id: I187901476f2728e4b7f72238e72006c95c188b55
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>