Support secgroups in Sahara Node group templates

Latest python-saharaclient (already in Heat dependencies) has ability
to provide security groups when creating node group templates.
This patch adds support for this feature to
OS::Sahara::NodeGroupTemplate resource in Heat.

Change-Id: I5f94366e1bb2db07b8f92ca8cabf4c4ecf5c3d51
Closes-Bug: #1379318
Merge "Support secgroups in Sahara Node group templates"