Update mysql cluster.cnf to match heat templates

In t-h-t I522b7324460469c59f49983ca3becd9ea914cdc0 some of the
parameters to mysql have been changed. We have changed cluster-name to
cluster_name and we are passing in a native list of control nodes rather
than computing the cluster address string in the heat template.

Change-Id: I810eaf18adfdfc321dfa78e6547890521c4cb726
Merge "Update mysql cluster.cnf to match heat templates"