mysql_tzinfo_to_sql tries to set wsrep_replicate_myisam
as SESSION variable, while its a GLOBAL-only system variable,
and thus the resulting sql would fail to load.

Fixed by changing the scope to GLOBAL in the SET command.

Also added following include files to facilitate testing :
* include/have_wsrep.inc
* include/not_wsrep.inc
* include/have_wsrep_enabled.inc