Fixes the following vet reports:

provisioner/salt-masterless/provisioner.go:119: arg cmd for printf verb %s of wrong type: *github.com/mitchellh/packer/packer.RemoteCmd
provisioner/salt-masterless/provisioner.go:121: arg err for printf verb %d of wrong type: error
provisioner/salt-masterless/provisioner.go:142: arg err for printf verb %d of wrong type: error
provisioner/salt-masterless/provisioner.go:157: arg err for printf verb %d of wrong type: error
provisioner/salt-masterless/provisioner.go:172: arg err for printf verb %d of wrong type: error
provisioner/salt-masterless/provisioner.go:216: arg err for printf verb %d of wrong type: error