Add miq_product_features to miq_group

[jntullo]

This adds miq_product_features to miq_group. This is needed for both ManageIQ/manageiq-api#311 as well as to expose the miq_groups via the api such as /api/groups/:id?attributes=miq_product_features

@miq-bot assign @gtanzillo
cc: @abellotti

[miq-bot]

Checked commit jntullo@b756550 with ruby 2.3.3, rubocop 0.52.0, haml-lint 0.20.0, and yamllint 1.10.0
1 file checked, 1 offense detected

app/models/miq_group.rb

• ❗ - Line 16, Col 3 - Rails/InverseOf - Specify an :inverse_of option.

[abellotti]

LGTM!! Thanks @jntullo 👍 just tried this from the API.