Add flag to set nova v3 api for tempest

This commit adds a new env variable, TEMPEST_NOVA_API_V3 to set
whether the tempest api v3 tests are enabled.

Change-Id: If14deb80f271061e70fae6c3d13b210ac0dd9399

Author: mtreinish

lib/tempest

@@ -283,6 +283,7 @@ function configure_tempest {
     iniset $TEMPEST_CONFIG compute ssh_connect_method $ssh_connect_method
 
     # Compute Features
+    iniset $TEMPEST_CONFIG compute-feature-enabled api_v3 ${TEMPEST_NOVA_API_V3:-False}
     iniset $TEMPEST_CONFIG compute-feature-enabled resize True
     iniset $TEMPEST_CONFIG compute-feature-enabled live_migration ${LIVE_MIGRATION_AVAILABLE:-False}
     iniset $TEMPEST_CONFIG compute-feature-enabled change_password False