Problem was that if wsrep_notify_cmd was set it was called
with a new status "joined" it tries to connect to the server
to update some table, but the server isn't initialized yet,
it's not listening for connections. So the server waits for the
script to finish, script waits for mariadb client to connect,
and the client cannot connect, because the server isn't listening.

Fix is to call script only when Galera has already formed a
view or when it is synched or donor.

This fix also enables following test cases:
* galera.MW-284
* galera.galera_binlog_checksum
* galera_var_notify_ssl_ipv6
Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>