Fix bug in checking of IDENTIFY_SYSTEM result.

5a991ef8692ed0d170b44958a81a6bd70e90585 added new column into
the result of IDENTIFY_SYSTEM command. But it was not reflected into
several codes checking that result. Specifically though the number of
columns in the result was increased to 4, it was still compared with 3
in some replication codes.

Back-patch to 9.4 where the number of columns in IDENTIFY_SYSTEM
result was increased.

Report from Michael Paquier