Galera startup crash fix, temporal removal of revert snapshot (Galera does not survive revert)

and add cores saving from tests themselves.

maxscale-system-test/mdbci/backend/create_repl_user.sql

@@ -1,4 +1,4 @@
-#create user repl@'%' identified by 'repl'; 
-grant replication slave on *.* to repl@'%' identified by 'repl'; 
+#create user repl@'%' identified by 'repl';
+grant replication slave on *.* to repl@'%' identified by 'repl';
 
 FLUSH PRIVILEGES;