Add "spot_price" param into template processing

builder/amazon/common/run_config.go

@@ -91,6 +91,7 @@ func (c *RunConfig) Prepare(t *packer.ConfigTemplate) []error {
 	templates := map[string]*string{
 		"iam_instance_profile":    &c.IamInstanceProfile,
 		"instance_type":           &c.InstanceType,
+		"spot_price":              &c.SpotPrice,
 		"ssh_timeout":             &c.RawSSHTimeout,
 		"ssh_username":            &c.SSHUsername,
 		"ssh_private_key_file":    &c.SSHPrivateKeyFile,