Add salt plugin
 - uses salt bootstrap to install minion code
 - custom grains can be set.
 - option to specify master in the manifest.

e.g manifest (TODO: Add this to doc.)

"salt": {
            "install_source": "git",
            "version": "develop", \\ Only if the source is git
            "master": "", \\ salt master ip or fqdn
            "grains": {
                "custom_grain1": "custom_grain_value1",
                "custom_grain2": "custom_grain_value2",
            }
        }
Merge pull request #84 from dbalan/saltstack_minion

Add salt plugin.