When using MyIsam tables and processing concurrent DML
statements, the server may be sending back an OK to the client
before actually finishing the transaction commit procedure. This
has been reported before in BUG@37521 and BUG@29334.

This particular test case gets affected, because it performs the
following sequence:
  
  connect (conn2, ...)
  connection conn2;
  LOAD DATA CONCURRENT ...
  disconnect (conn2, ...)
  connection master;
  sync_slave_with_master
  diff_tables

At this point diff_tables may report difference in the table
content (the master seems to be missing the conn2 rows). 

To workaround this MyISAM concurrent DML statements issue and
make this test case deterministic, we wait on conn2 until the
rows inserted show up in the table. After this the test case
proceeds as normally would before this patch.