As test directories contain a space, we need to
properly quote paths, otherwise we get errors like:

```
umount: /home/christian/gocode/src/github.com/ipfs/go-ipfs/test/sharness/trash is not mounted (according to mtab)
umount: /home/christian/gocode/src/github.com/ipfs/go-ipfs/test/sharness/trash is not mounted (according to mtab)
```

instead of:

```
umount: /home/christian/gocode/src/github.com/ipfs/go-ipfs/test/sharness/trash directory.t0030-mount.sh/ipfs is not mounted (according to mtab)
umount: /home/christian/gocode/src/github.com/ipfs/go-ipfs/test/sharness/trash directory.t0030-mount.sh/ipns is not mounted (according to mtab)
```

License: MIT
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>