fixing ``platform_opt`` to ``platform_option``

we broke starring a bit ago because we stopped doing a ``_.extend`` on job detail to the stored job in resultset model.  This extend was hiding the fact that the ``resultset`` endpoint was returning this field as ``platform_option`` but the ``jobs`` endpoint was returning it as ``platform_opt``.  It also returns ``result_set_id`` with the resultset endpoint as another part of the bug.

So this is the service portion that standardizes on ``platform_option``.  

The companion ui pr is: https://github.com/mozilla/treeherder-ui/pull/57