Root of problem was that HTON_NO_BINLOG_ROW_FORMAT was ignored when 
writing RB Binlog events, causing binlog events to be missing relevant
info affecting the conflict detection testcases.

Fix to Binlogging code has been pushed to mysql-5.6 + mysql-trunk, cherry
picked back into mysql-5.6-cluster-7.3.

This patch modifies the conflict detection code to be more strict about
having the necessary columns to perform conflict detection.

The existing conflict detection testcases are modified to check the 
behaviour is as expected.

A new testcase is added to check the original problem with 
binlog-row-image=minimal.