Remove reference to root group

By not specifying it, root user's group should be used.
Merge pull request #15 from alanpearce/root-group

Remove reference to root group
Config: Refactor host key provisioning into loop
Config: Add support for ECDSA host keys
Update pillar.example
Merge pull request #16 from alanpearce/ecdsa

Add support for ECDSA host keys
Config: Add support for generating keys
Update pillar example
Merge pull request #17 from alanpearce/generate-keys

Config: Add support for generating keys