Do not execute drush-site-install when importing and existing database

drush-site-install errors out when trying to import an existing database.

in .drush_lamp.json
```json
{
  "drupal": {
    "sites": {
      "mysite": {
        "deploy": true,
        "clean": true,
        "releases": 1,
        "files": "sites/default/files",
        "settings": "sites/default/settings.php",
        "repository": {
          "uri": "git@github.com:draenen/mysite.git",
          "revision": "master"
        },
        "database": "mysite.sql"
      }
    }
  }
}
```

Error:
```
[2013-07-03T16:02:46+00:00] INFO: Processing execute[drush-site-install] action run (/tmp/vagrant-chef-1/chef-solo-1/cookbooks/drupal/recipes/default.rb line 112)

================================================================================
Error executing action `run` on resource 'execute[drush-site-install]'
================================================================================

Errno::ENOENT
-------------
No such file or directory - drush-site-install
```