Change auth_version to v3 on Tempest

Keystone v3 API is CURRENT and the v2 API is deprecated now.
So we need to change the default config of auth_version to fit
for current API status.

Depends-On: Id5e5ed9bf4f8b0f9eb376bfc7c5801f0956da1d9
Change-Id: I801e6740258ddea2a1b628a209970e0307d39d12
diff --git a/lib/tempest b/lib/tempest
index d95a9f5..b48dd07 100644
--- a/lib/tempest
+++ b/lib/tempest
@@ -273,13 +273,11 @@
     if [ "$ENABLE_IDENTITY_V2" == "True" ]; then
         # Run Identity API v2 tests ONLY if needed
         iniset $TEMPEST_CONFIG identity-feature-enabled api_v2 True
-        iniset $TEMPEST_CONFIG identity auth_version ${TEMPEST_AUTH_VERSION:-v2}
     else
         # Skip Identity API v2 tests by default
         iniset $TEMPEST_CONFIG identity-feature-enabled api_v2 False
-        # Use v3 auth tokens for running all Tempest tests
-        iniset $TEMPEST_CONFIG identity auth_version v3
     fi
+    iniset $TEMPEST_CONFIG identity auth_version ${TEMPEST_AUTH_VERSION:-v3}
 
     if is_ssl_enabled_service "key" || is_service_enabled tls-proxy; then
         iniset $TEMPEST_CONFIG identity ca_certificates_file $SSL_BUNDLE_FILE