Disable persistent_cache.test due to upstream MyRocks issue #579.

Author: spetrunia

storage/rocksdb/mysql-test/rocksdb/t/disabled.def

@@ -45,6 +45,8 @@ rpl_row_not_found : MariaDB doesnt support slave_exec_mode='SEMI_STRICT'
 
 blind_delete_without_tx_api: MDEV-12286: rocksdb.blind_delete_without_tx_api test fails
 
+persistent_cache: Upstream RocksDB bug https://github.com/facebook/mysql-5.6/issues/579
+
 allow_no_pk_concurrent_insert: stress test
 rocksdb_deadlock_stress_rc: stress test
 rocksdb_deadlock_stress_rr: stress test