Update multi.md

Removed quotes around the directory names, riak creates directories with quotes if you do so, and in a really wierd way, perhaps it should be reported as a bug to cuttlefish or riak kv ?

Having followed the instructions, with a data directory - `"/var/lib/riak/bitcask"`.

Also renamed the data storage directories to reflect their connection with the name, as discussed, might do some more work on this page.


I found it necessary to remove the created directory, which was under a directory relative to Riak.

```
rm -rf \"*
```

Corrected typo bitcask -> leveldb
Merge pull request #1364 from basho/fix-multi-backend-config-example

Update multi.md