add common commHost function

helper/communicator/comm_host.go

@@ -0,0 +1,22 @@
+package communicator
+
+import (
+	"log"
+
+	"github.com/hashicorp/packer/helper/multistep"
+)
+
+// Generic commHost function that should work for most cloud builders.
+func CommHost(host string, statebagKey string) func(multistep.StateBag) (string, error) {
+	return func(state multistep.StateBag) (string, error) {
+		if host != "" {
+			log.Printf("Using ssh_host value: %s", host)
+			return host, nil
+		}
+		ipAddress, hasIP := state.Get(statebagKey).(string)
+		if !hasIP {
+			return "", fmt.Errorf("Failed to retrieve IP address.")
+		}
+		return ipAddress, nil
+	}
+}