This is faster under gdb/valgrind (this should speed up work of people who have to run
a simple test 50 times to do debugging). Running without --big, which is the default, InnoDB tests
take at most 18MB so 128 was overkill. Running with --big, InnoDB tests take 450MB so 128
was not enough anyway.


mysql-test/mysql-test-run.pl:
  10M is faster to create than 128M (especially under gdb or valgrind) and is enough for most tests.