add test for adding instructors to Owners
full test coverage for create_teams
split create_teams into smaller methods
simplify logic around team creation
unify logic around adding users to teams
simplify CreateTeams#add_members
make a fixture_path() method
read_file() doesn't need to know the type of file
add spec for read_file()
fix create_teams for groups of students
Merge pull request #66 from education/create-teams-refactor

Refactor create_teams