Mark rocksdb.bulk_load and rocksdb.add_index_inplace_sstfilewriter as big

They use much more disk space than all other tests in rocksdb test suite

storage/rocksdb/mysql-test/rocksdb/t/add_index_inplace_sstfilewriter.test

 --source include/have_rocksdb.inc
 
+# This test requires ~1.3G of disk space
+--source include/big_test.inc
+
 --disable_warnings
 drop table if exists t1;
 --enable_warnings

storage/rocksdb/mysql-test/rocksdb/t/bulk_load.test

 --source include/have_rocksdb.inc
 --source include/have_partition.inc
 
+# This test requires ~2.3G of disk space
+--source include/big_test.inc
+
 --disable_warnings
 DROP TABLE IF EXISTS t1, t2, t3;
 --enable_warnings