Fix sporadic failure for MTR test galera_sr.GCF-1018B. The test
sometimes fails due to an error that is logged to the error log
unnecessarily.
A deterministic test case (included in this patch) shows that the
error is loggen when a transaction is BF aborted right before  it
opens the streaming log table to perform fragment removal. When that
happens, the attempt to open the table fails and consequently an error
is logged. There is no need to log this error, as an ER_LOCK_DEADLOCK
error is returned to the client.
Reviewed-by: Jan Lindström <jan.lindstrom@mariadb.com>