Merge PR #22838 into master

* refs/pull/22838/head:
	kv/RocksDBStore: Handle nullptr if clock cache is chosen.
	kv/rocksdb_cache/BinnedLRUCache: Don't promote data to the high pri pool.
	src/kv: Initial import of a custom RocksDB cache.
	src/rocksdb: switch back to master branch.

Reviewed-by: Sage Weil <sage@redhat.com>

diff --cc src/common/options.cc
Simple merge

diff --cc src/kv/CMakeLists.txt
Simple merge

diff --cc src/kv/RocksDBStore.cc
Simple merge