Avoid deleting the .baseline folder when destroying the VM

I thought it could make sense that someone would destroy the VM just to create it again.

While creating a VM, something failed. I wouldn't trust the state of it and I went ahead to send it to the graveyard of VMs with:

```
baseline destroy
```

Pretty awesome so far. However, when I 'upped' it again with:

```
baseline up whatever
```

the process failed. .baseline had been removed and I had to:

```
baseline init
```

That means that, if I were working on a Vagrantfile and that hadn't been pushed to a repo, I'd miss my changes, right?

So I modified the destroy command so that it doesn't erase .baseline folder, and created a 'cleanup' command that, guess what, cleans up the .baseline folder.

How does it sound like?

Hugs from China!