Use the workspace cache.

The update vm job was caching git repos, but the gate job wasn't
using them.

Change-Id: I20d6bed6724ef131109fe3ccfe2b11e34edc8a96

devstack-vm-gate-wrap.sh

@@ -60,6 +60,12 @@ function setup_workspace {
     sudo chown -R jenkins:jenkins $DEST
     cd $DEST
 
+    # The vm template update job should cache the git repos
+    # Move them to where we expect:
+    if ls ~/workspace-cache/*; then
+      mv ~/workspace-cache/* $DEST
+    fi
+
     ORIGINAL_GERRIT_PROJECT=$GERRIT_PROJECT
     ORIGINAL_GERRIT_BRANCH=$GERRIT_BRANCH