fixes #3071 - OS edit failed on foreign keys since config_template_id was '0' on blank

[isratrade]

No description provided.

[isratrade]

The previous code passed config_template_id => '0' if selectbox was blank. Not is it null, so the following code below works.

  accepts_nested_attributes_for :os_default_templates, :allow_destroy => true,
    :reject_if => lambda { |v| v[:config_template_id].blank? }

[domcleal]

Under test: http://ci.theforeman.org/job/test_develop_integration/6/

[domcleal]

Merged as f76e5ee, thanks @isratrade!