Use chelper generate_ha_relation_data for ha rel

Use the generate_ha_relation_data helper from charmhelpers to
generate the data to send down the relation to the hacluster
charm.

This results in a few changes in behaviour:

1) The charm will no longer specify a nic name to bind the vip. This
   is because Pacemaker VIP resources are able to automatically
   detect and configure correct iface and netmask parameters based
   on local configuration of the unit.
2) The original iface named VIP resource will be stopped and deleted
   prior to the creation of the new short hash named VIP resource.

Change-Id: I6c10762e4f3367684f19852d03d5e5b84cf37600