test-admin-deploy-var: Don't rely on OSTREE_FEATURES

This is set during build-time testing, but unset during "as-installed"
tests.

Resolves: #3183
Signed-off-by: Simon McVittie <smcv@debian.org>

tests/test-admin-deploy-var.sh

@@ -21,7 +21,7 @@ set -euox pipefail
 
 . $(dirname $0)/libtest.sh
 
-if ! echo "$OSTREE_FEATURES" | grep --quiet --no-messages "initial-var"; then
+if ! ${CMD_PREFIX} ostree --version | grep --quiet --no-messages -e "- initial-var"; then
     fatal missing initial-var
 fi