[Sahara] Added ability to specify security groups for node group

Known issues:
1. Security groups added to the same page as general parameters. Page
   is a little overloaded now. Will improve this later.

Change-Id: Ieb224ea4db2adc46073b86e7181981ea598c9a8f
Blueprint: cluster-secgroups
Closes-Bug: #1364659
Merge "[Sahara] Added ability to specify security groups for node group"