Add description for SSL options.
Replace wsrep_cluster_address with wsrep_cluster_members

The wsrep_cluster_members parameter is an array of IP addresses or
hostnames of one or more members of the cluster. This replaces the old
wsrep_cluster_address parameter, which was simply a string passed
directly to the template.
Add bootstrap parameter

When set to true, the wsrep_cluster_address set by the erb template
will be "gcomm://". If false, the wsrep_cluster_address will use the
list of node specified by wsrep_cluster_members.