Fixed error in ext_pillar() params

The minion_id param was not necessisary and was causing errors.
I also updated the docs to properly evaluate the yaml, and added
additional exception handling.
Merge branch 'develop' of github.com:saltstack/salt into bugfix/django_orm
Merge pull request #7418 from micahhausler/bugfix/django_orm

Fixed param error in django_orm ext_pillar