The issue is that xa.test failed sporadically on some platforms.
The reason for the test failure is a race condition in xa.test.
The race condition occures between connection that executes statement
INSERT INTO t2 SELECT FROM t1 and other connection that tries to run
statements DELETE FROM t1 and COMMIT. If COMMIT statement had been executed
before the statement INSERT INTO t2 SELECT FROM t1 was locked by lock
on table t1 (as a result of query from table t1) then the INSERT statement
is executed successfully and a following test for deadlock would failed.

This patch fixes this race condition by moving COMMIT statement after commit
of distributed transaction from concurrent session.