Adjust blockstore open logs to say blockstore instead of database

[steviez]

Problem

Grepping logs, one is probably inclined to search for blockstore (the name of the higher level object in the source code) instead of database.

Summary of Changes

• Use blockstore in place of database
• Make the log after the open operation more similar to one prior to make it more clear that they are the before/after

Before this PR:

[...  solana_ledger::blockstore] Opening database at "/home/sol/ledger/rocksdb
[...  solana_ledger::blockstore] "/home/sol/ledger/rocksdb" open took 895ms

And after this PR:

[...  solana_ledger::blockstore] Opening blockstore at "/home/sol/ledger/rocksdb
[...  solana_ledger::blockstore] Opening blockstore done; blockstore open took 895ms

[steviez]

@t-nelson - Adding you as I think we have shared similar disdain for "asymmetric" starting/done logs elsewhere in the codebase

[codecov]

Codecov Report

Attention: 521 lines in your changes are missing coverage. Please review.

Comparison is base (835183a) 81.8% compared to head (eb31176) 81.8%.
Report is 1674 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #34672      +/-   ##
==========================================
  Coverage    81.8%    81.8%              
==========================================
  Files         767      824      +57     
  Lines      209297   222488   +13191     
==========================================
+ Hits       171276   182119   +10843     
- Misses      38021    40369    +2348     

[t-nelson]