Galera strict mode

Add configuration variable wsrep_strict_mode=[ON|OFF] where operations that are harmful or problematic in cluster environment are either refused with an error message or produce a warning.

Jan's suggested ideas:

• A session has binlog_format set to STATEMENT, and the session writes to an InnoDB table. The associated statement will be logged in statement-based format, which is unsupported by Galera,
• A session has binlog_format set to MIXED, and the session writes to an InnoDB table. The associated statement could be logged in statement-based format, which is unsupported by Galera.
• A node has wsrep_replicate_myisam set to OFF, and a session on the node writes to a MyISAM table, so the write will not be replicated.
• A node has wsrep_replicate_aria set to OFF, and a session on the node writes to an Aria table, so the write will not be replicated.
• A session writes to any other non-InnoDB storage engine, so the write will not be replicated.
• A session has wsrep_on set to OFF, and the session writes to an InnoDB table, so the write will not be replicated.

Approach used for the implementation:
wsrep_mode is a server variable that one can use to enable/disable specific Galera features.
To set or unset the various features, use the following syntax:

SET GLOBAL wsrep_mode='cmd[,cmd]...';

Possible values:

• DEFAULT : Disable all features
• BINLOG_ROW_FORMAT_ONLY : Galera requires binlog format row
• REQUIRED_PRIMARY_KEY : Galera will require primary key for tables
• STRICT_REPLICATION : Warning is issued if changes are done to tables that storage engine is not supported by Galera

Variable wsrep_strict_ddl is deprecated and replaced with wsrep_mode='STRICT_REPLICATION'.