Setting a nae for the the THD::security_ctx:user field for wsrep applier threads.
With this, the audit log events related to wsrep applying will be written in the
audit log.
Using user name <cluster user> for wsrep appliers. This is for having identical
look with async replication, which uses: <replication_user> user name.
Another option for <cluster user> could be e.g. <wsrep user>. Hoever, using galera
for user name is not a good pick, as the cluster may have (and soon will have)
other GCS backends.
Using same approach as async replication to replace the security_ctx user name
with "system user" for processlist output.
Commit has also mtr test galera.MDEV-35511, to vevrify wsrep applier audit logging.
The test does not install/uninstall audit log plugin, bu loads the audit log plugin
before the test. This is because uninstalling the audit log plugin gives a warning
saying that plugin is busy and uninstall will be delayed until server shutdown.
This anomaly must be because of the applier thread being active audit logger.
Same problem with plugin unsinstall happens also with async relication workers.
If plugn remains installed, the post test sanity check will complain of mismatching
state of pre and post test states.
41a2ccc94a