Add OSX specific file extensions to gitignore
Add OSX specific file extensions to gitignore

Added a section to the proejct .gitignore file to add
OSX specific file extensions to. Added the primary
extension that causes issues i.e., .DS_Store which
gets added by the OSX Finder utility.

Change-Id: Ic78f8e367e2401868c7df1b49ef72f57f5cc3011

openstack/tosca-parser,openstack/tosca-parser