The test assumes that `@@global.auto_increment_offset` is equal to
`wsrep_local_index + 1`. Which is normally the case if galera runs
with option `wsrep_auto_increment_control` enabled.
However, if some prior test performs a restart of a server, then
`wsrep_local_index` may change, and galera will set the value of
`auto_increment_offset` accordingly.
However, if `auto_increment_offset` changes during a test run, then
mtr will complain. To avoid that, tests that perform restarts include
`auto_increment_offset_save.inc` and `auto_increment_offset_restore.inc`.
Which reset the value of `auto_increment_offset`. And when that
happens, `auto_increment_offset` will no longer be equal to
`wsrep_local_index + 1`, and the test fails.
To avoid this problem, simply check that the offsets are different
on the nodes that compose the cluster.