Do not fetch the latest header BID on persistent snapshot creation
Do not fetch the latest header BID on persistent snapshot creation

- On snapshot creation, we don't need to scan until we meet the latest
header. Just stop at the header corresponding to the snapshot.

- This change does not affect any DB semantics; just removing an
inefficiency.

Change-Id: I02cc4af2ad986df2a483876c561268bd994ff12a

couchbase/forestdb,wurikiji/forestdb,wurikiji/forestdb,couchbase/forestdb,hisundar/forestdb,hisundar/forestdb