Create galera_recovery_information script for systemd Galera systems

Hi,

We need a script in systemd installations that does --wsrep_recover. Before systemd we could do:
service mysqld start --wsrep_recover. The script is similar in nature to galera_new_cluster.

I have put this issue to critical because we just added this script into training materials, due to be delivered in 2 weeks.

Cheers,
Michaël