Trivial fixes from review of os-test-images

This fixes some trivial things from the review where this support was
added:

https://review.opendev.org/c/openstack/devstack/+/925425

Change-Id: I990a3816f425a1b4c8680ec43d698e32eea2238b
diff --git a/stackrc b/stackrc
index 0492c73..0b3e1c6 100644
--- a/stackrc
+++ b/stackrc
@@ -304,6 +304,9 @@
 TEMPEST_BRANCH=${TEMPEST_BRANCH:-$BRANCHLESS_TARGET_BRANCH}
 TEMPEST_VENV_UPPER_CONSTRAINTS=${TEMPEST_VENV_UPPER_CONSTRAINTS:-master}
 
+OSTESTIMAGES_REPO=${OSTESTIMAGES_REPO:-${GIT_BASE}/openstack/os-test-images.git}
+OSTESTIMAGES_BRANCH=${OSTESTIMAGES_BRANCH:-$BRANCHLESS_TARGET_BRANCH}
+OSTESTIMAGES_DIR=${DEST}/os-test-images
 
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