When the change buffer records for a page span across multiple change
buffer leaf pages or the starting record is at the beginning of a page
with a left sibling, ibuf_delete_recs deletes only the records in first
page and fails to move to subsequent pages.

Subsequently a slow shutdown hangs trying to delete those left over
records.

Fix-A: Position the cursor to an user record in B-tree and exit only
when all records are exhausted.

Fix-B: Make sure we call ibuf_delete_recs during slow shutdown for
pages with IBUF entries to cleanup any previously left over records.