Upgrade to RocksDB 5.8.8 and tune settings to reduce space amplification (#7348)

* kvdb-rocksdb: update to RocksDB 5.8.8

* kvdb-rocksdb: tune RocksDB options

* Switch to level-style compaction
* Increase default block size (16K), and use bigger blocks for HDDs (64K)
* Increase default file size base (64MB SSDs, 256MB HDDs)
* Create a single block cache shared across all column families
* Tune compaction settings using RocksDB helper functions, taking into account
  memory budget spread across all columns
* Configure backgrounds jobs based on the number of CPUs
* Set some default recommended settings

* ethcore: remove unused config blockchain.db_cache_size

* parity: increase default value for db_cache_size

* kvdb-rocksdb: enable compression on all levels

* kvdb-rocksdb: set global db_write_bufer_size

* kvdb-rocksdb: reduce db_write_bufer_size to force earlier flushing

* kvdb-rocksdb: use master branch for rust-rocksdb dependency

parity/cli/mod.rs

@@ -779,7 +779,7 @@ usage! {
 			"--pruning-memory=[MB]",
 			"The ideal amount of memory in megabytes to use to store recent states. As many states as possible will be kept within this limit, and at least --pruning-history states will always be kept.",
 
-			ARG arg_cache_size_db: (u32) = 32u32, or |c: &Config| otry!(c.footprint).cache_size_db.clone(),
+			ARG arg_cache_size_db: (u32) = 128u32, or |c: &Config| otry!(c.footprint).cache_size_db.clone(),
 			"--cache-size-db=[MB]",
 			"Override database cache size.",
 
@@ -1797,7 +1797,7 @@ mod tests {
 				pruning_memory: None,
 				fast_and_loose: None,
 				cache_size: None,
-				cache_size_db: Some(128),
+				cache_size_db: Some(256),
 				cache_size_blocks: Some(16),
 				cache_size_queue: Some(100),
 				cache_size_state: Some(25),