test: do not remove state directory on failure

The test log is in the state directory, and we want to keep it around
when a test fails.

Follow-up for: 256a835f1c

(cherry picked from commit 49e8342965)
(cherry picked from commit dbb1b9c2c8)

test/test-functions

@@ -3209,7 +3209,8 @@ do_test() {
                 fi
                 test_cleanup
                 if [ $ret -eq 0 ]; then
-                    rm "$TESTLOG"
+                    # $TESTLOG is in $STATEDIR, so clean it up only on success
+                    [[ -n "$STATEDIR" ]] && rm -vfr "$STATEDIR"
                     echo "[OK]"
                 else
                     echo "[FAILED]"