MB-15254 Use separate forestdb file handle for compaction
MB-15254 Use separate forestdb file handle for compaction

Forestdb doesn't allow sharing of file handles across fdb_commit and
fdb_compact. So a separate file handle is required. The advisory lock
on the same handle leads to lot of contention between commit and compact.

GetAllSnapMarkers will also be using this new handle to avoid any lock contention.

Change-Id: I200ff4430a922d5f950f3fa73f87a247b0cbb7cd

jchris/indexing,jchris/indexing,jchris/indexing,jchris/indexing