Support opening an in-use rocksdb as secondary (bp #10209)

[mergify]

This is an automated backport of pull request #10209 done by Mergify

Cherry-pick of caa7f7a has failed:

On branch mergify/bp/v1.1/pr-10209
Your branch is up to date with 'origin/v1.1'.

You are currently cherry-picking commit caa7f7a0c.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:

	modified:   Cargo.lock
	modified:   genesis/src/main.rs
	modified:   ledger/src/blockstore.rs
	modified:   ledger/src/blockstore_db.rs
	modified:   ledger/src/blockstore_processor.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)

	both modified:   ledger-tool/Cargo.toml
	both modified:   ledger-tool/src/main.rs

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[solana-grimes]

💔 Unable to automerge due to CI failure

[codecov]

Codecov Report

Merging #10381 into v1.1 will increase coverage by 0.0%.
The diff coverage is 68.1%.

@@          Coverage Diff           @@
##            v1.1   #10381   +/-   ##
======================================
  Coverage   80.6%    80.7%           
======================================
  Files        289      289           
  Lines      66881    66923   +42     
======================================
+ Hits       53955    54033   +78     
+ Misses     12926    12890   -36