Fix example of image building for heat
Fix example of image building for heat

The example that shows how to build an image is incorrect.
It lacks heat-config element in disk-builder command.
Without this element software deployment  doesn't work with heat.

Change-Id: I53a145ed532a0baba2c28b889001728911b4d266

bbandaru/heat-templates,cosminmocan/heat-templates,bbandaru/heat-templates,wesparish/heat-templates,wesparish/heat-templates,openstack/heat-templates,bbandaru/heat-templates,kwrobert/heat-templates,wesparish/heat-templates,bbandaru/heat-templates,kwrobert/heat-templates,cosminmocan/heat-templates,openstack/heat-templates,kwrobert/heat-templates,cosminmocan/heat-templates,kwrobert/heat-templates,tgreenyc/heat-templates,tgreenyc/heat-templates,tgreenyc/heat-templates,openstack/heat-templates,tgreenyc/heat-templates,wesparish/heat-templates,cosminmocan/heat-templates