Make tmp directory

Before
------

```
% ./bin/test-mysql setup
/home/megurine/test-mysql/lib/test-mysql/manager.rb:77:in `initialize': No such file or directory - /home/megurine/test-mysql/tmp/my.cnf (Errno::ENOENT)
        from /home/megurine/test-mysql/lib/test-mysql/manager.rb:77:in `open'
        from /home/megurine/test-mysql/lib/test-mysql/manager.rb:77:in `setup'
        from ./bin/test-mysql:127:in `block in <main>'
        from /usr/local/rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/optparse.rb:1412:in `call'
        from /usr/local/rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/optparse.rb:1412:in `block in parse_in_order'
        from /usr/local/rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/optparse.rb:648:in `search'
        from /usr/local/rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/optparse.rb:1510:in `block in visit'
        from /usr/local/rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/optparse.rb:1509:in `reverse_each'
        from /usr/local/rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/optparse.rb:1509:in `visit'
        from /usr/local/rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/optparse.rb:1412:in `parse_in_order'
        from /usr/local/rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/optparse.rb:1341:in `order!'
        from /usr/local/rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/optparse.rb:1432:in `permute!'
        from /usr/local/rbenv/versions/1.9.3-p194/lib/ruby/1.9.1/optparse.rb:1453:in `parse!'
        from ./bin/test-mysql:154:in `<main>'
```

After
-----

```
% ./bin/test-mysql setup
user database and tmp/my.cnf are initialized.
```