Change "user" to "admin" in course team BDD descriptions

cms/djangoapps/contentstore/features/course-team.feature

 Feature: Course Team
     As a course author, I want to be able to add others to my team
 
-    Scenario: Users can add other users
+    Scenario: Admins can add other users
         Given I have opened a new course in Studio
         And the user "alice" exists
         And I am viewing the course team settings
@@ -9,7 +9,7 @@ Feature: Course Team
         And "alice" logs in
         Then she does see the course on her page
 
-    Scenario: Added users cannot delete or add other users
+    Scenario: Added admins cannot delete or add other users
         Given I have opened a new course in Studio
         And the user "bob" exists
         And I am viewing the course team settings
@@ -18,7 +18,7 @@ Feature: Course Team
         Then he cannot delete users
         And he cannot add users
 
-    Scenario: Users can delete other users
+    Scenario: Admins can delete other users
         Given I have opened a new course in Studio
         And the user "carol" exists
         And I am viewing the course team settings
@@ -27,7 +27,7 @@ Feature: Course Team
         And "carol" logs in
         Then she does not see the course on her page
 
-    Scenario: Users cannot add users that do not exist
+    Scenario: Admins cannot add users that do not exist
         Given I have opened a new course in Studio
         And I am viewing the course team settings
         When I add "dennis" to the course team