Support Keystone V3 based gate

Introduces a new variable DEVSTACK_GATE_KEYSTONE_V3 to enable
keystone v3 based gate run.

For now enabling this only configures tempest to use keystone v3.

Partially implements bp multi-keystone-api-version-tests

Change-Id: Ib423386a7772e06f028403ab092eb04ee1b1f875

devstack-vm-gate-wrap.sh

@@ -171,6 +171,9 @@ export DEVSTACK_GATE_MARCONI=${DEVSTACK_GATE_MARCONI:-0}
 # Set to 0 to disable config_drive and use the metadata server instead
 export DEVSTACK_GATE_CONFIGDRIVE=${DEVSTACK_GATE_CONFIGDRIVE:-1}
 
+# Set to 1 to enable running a keystone v3 based gate
+export DEVSTACK_GATE_KEYSTONE_V3=${DEVSTACK_GATE_KEYSTONE_V3:-0}
+
 # Set the number of threads to run tempest with
 DEFAULT_CONCURRENCY=$(nproc)
 if [ ${DEFAULT_CONCURRENCY} > 3 ] ; then

devstack-vm-gate.sh

@@ -237,6 +237,11 @@ EOF
     else
         echo "FORCE_CONFIG_DRIVE=False" >>localrc
     fi
+    if [ "$DEVSTACK_GATE_KEYSTONE_V3" -eq "1" ]; then
+        # Run gate using only keystone v3
+        # For now this is only injected in tempest configuration
+        echo "TEMPEST_AUTH_VERSION=v3" >>localrc
+    fi
 }
 
 if [ "$DEVSTACK_GATE_GRENADE" -eq "1" ]; then