Rename bad option value

To disable tempest running the v2 tests when the identity v2 api is
disabled you need to set api_v2=False not v2_api=False.

Change-Id: Ied8a0593619dccb5985f9a1e51feb370754336c7

Author: Jamie Lennox

lib/tempest

@@ -323,7 +323,7 @@ function configure_tempest {
     fi
     if [ "$ENABLE_IDENTITY_V2" == "False" ]; then
         # Only Identity v3 is available; then skip Identity API v2 tests
-        iniset $TEMPEST_CONFIG identity-feature-enabled v2_api False
+        iniset $TEMPEST_CONFIG identity-feature-enabled api_v2 False
         # In addition, use v3 auth tokens for running all Tempest tests
         iniset $TEMPEST_CONFIG identity auth_version v3
     else