MDEV-26223 Galera cluster node consider old server_id value even after modification of server_id [wsrep_gtid_mode=ON]

Variable `wsrep_new_cluster` now will be TRUE also when there is only `gcomm://` used
in configuration. This configuration, even without --wsrep-new-cluster,
is considered to bootstrap new cluster.

Updated galera GTID test to ignore warning message when non bootstrap
node have server-id different thant one cluster is initialized with.
Reviewed-by: Jan Lindström <jan.lindstrom@mariadb.com>