Do not give warnings about #rocksdb directory information_schema

"select * from information_schema.tables limit 1" was giving the following
warning in the log:

[ERROR] Invalid (old?) table or database name '#rocksdb'

sql/handler.cc

@@ -6580,7 +6580,7 @@ bool Discovered_table_list::add_file(const char *fname)
 {
   bool is_temp= strncmp(fname, STRING_WITH_LEN(tmp_file_prefix)) == 0;
 
-  if (is_temp && !with_temps)
+  if ((is_temp && !with_temps) || !strncmp(fname,STRING_WITH_LEN(ROCKSDB_DIRECTORY_NAME)))
     return 0;
 
   char tname[SAFE_NAME_LEN + 1];

sql/table.h

@@ -92,6 +92,7 @@ typedef ulonglong nested_join_map;
 #define tmp_file_prefix "#sql"			/**< Prefix for tmp tables */
 #define tmp_file_prefix_length 4
 #define TMP_TABLE_KEY_EXTRA 8
+#define ROCKSDB_DIRECTORY_NAME "#rocksdb"
 
 /**
   Enumerate possible types of a table from re-execution