Per discussions, for the purposes of the teams API, an 'instructor'
is any of:
	-course staff
	-global staff
	-discussion privileged users
This change will include the last case, which previously did not have
instructor access. Changes will be documented on the teams API wiki:
https://openedx.atlassian.net/wiki/display/TNL/Team+API

Tests have also been added to confirm this functionality.

TNL-2984