Try to combine __wt_hs_verify_one and __hs_verify_id

jie.chen@mongodb.com suggested a follow-up work here. I will try to summarize the idea:

• The goal is to re-use the code and make __wt_hs_verify use __wt_hs_verify_one
• __wt_hs_verify_one could take two new arguments: a hs cursor and a ds cursor. If those are NULL, open them. If not, reuse them.
  • This way, we could call __wt_hs_verify_one from __wt_hs_verify. Since __wt_hs_verify opens those two cursors already, we could pass them to the new __wt_hs_verify_one.

If this makes the design cleaner, easier to understand and to test, we should proceed.