[WIP] provisioner/salt-masterless Added option to apply grains before running highstate.

This *WIP* PR is to allows for the setting of grains within packer templates. This approach allows better control over the selection of states applied during highstate runs. 

Using this option will allow for the following to be usable in a salt `top.sls`:

```yaml
base:
  '*':
    - core
    - apt
  'app:myawesomeapp':
    - match: grain
    - awesomeapp
```

WIP will be removed once:
  - [ ] there's testing around the grains config
  - [ ] docs updated