Add InstructorCreatorCreateInstructorTest (unfinished), Modify InstructorCreator, Modify CreateInstructorResponse, Add Instructor Validator
Modify InstructorCreatorCreateInstructorTest and Add InstructorValidator
Merge remote-tracking branch 'carlos/master' into sprint_3_integration
Remove failing test with incorrect assertion

Remove a failing test which seems to be asserting that "guy" is an
invalid username - not sure why.
Fix error messages in InstructorValidator