Secure the MySQL bind-address on the seed

The MySQL bind-address on the seed should be set to
localhost for security.  Introduce a mysql.bind_address
to configure this for the seed. (mysql.local_bind sets
the bind address to the local IP for the overcloud)

Change-Id: I7faa97243c9a686badd8d11ec001480ecab4af50
Merge "Secure the MySQL bind-address on the seed"