Merge 'Clear test db's WAL too in clone_test_db.sh' from Jussi Saurio

Before #1570 , we never read anything from the on-disk WAL at startup,
so the `test_wal_frame_count()` test assertion `frame_count == 0`would
always pass, regardless of whether there was anything in the WAL or not
Now that the actual bug is fixed, the current test isn't idempotent
because the `clone_test_db.sh` command does not clear the wal, just the
db file

Closes #1581

scripts/clone_test_db.sh

@@ -1,3 +1,3 @@
 #!/bin/bash
-rm -f testing/testing_clone.db
+rm -f testing/testing_clone.db*
 sqlite3 testing/testing/db '.clone testing/testing_clone.db' > /dev/null