as well as

MDEV-19500 Update with join stopped worked if there is a call to a procedure in a trigger
MDEV-19521 Update Table Fails with Trigger and Stored Function
MDEV-19497 Replication stops because table not found
MDEV-19527 UPDATE + JOIN + TRIGGERS = table doesn't exists error

Reimplement the fix for (5d510fdb)

MDEV-18507 can't update temporary table when joined with table with triggers on read-only

instead of calling open_tables() twice, put multi-update
prepare code inside open_tables() loop.

Add a test for a MDL backoff-and-retry loop inside open_tables()
across multi-update prepare code.