Validate ip_version_for_ssh

Change-Id: Id016a8a7cbb61c186ee553c73ac00e2ba7c13a77
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>
diff --git a/heat_tempest_plugin/config.py b/heat_tempest_plugin/config.py
index 877574f..4992f17 100644
--- a/heat_tempest_plugin/config.py
+++ b/heat_tempest_plugin/config.py
@@ -128,6 +128,7 @@
                     "succeed."),
     cfg.IntOpt('ip_version_for_ssh',
                default=4,
+               choices=[4, 6],
                help="IP version used for SSH connections."),
     cfg.IntOpt('ssh_channel_timeout',
                default=60,