VM Memory is MB, not KB

This commit addresses the log message when configuring VM memory.

Wrong:

```
INFO -- : putting 4096KB memory into VM
```

Right:

```
INFO -- : putting 4096MB memory into VM
```

This should avoid me thinking that I have just created a VM with 4MB of
memory...
Merge pull request #32 from alphagov/doc-fix

VM Memory is MB, not KB