Clean up some instructor dash code
Adds Staff and Instructor factories
Removed duplicate code
Fix instructor api tests
Merge pull request #1589 from edx/flowerhack/fix/remove-duplicate-course-helper-code

Removed duplicate code
If the YouTube API JS fails to load, the rest of the JS should still run

Fixes BLD-472
Merge pull request #1579 from edx/sarina/enhance-user-factories

Sarina/enhance user factories
Merge pull request #1590 from edx/db/youtube-fallback

If the YouTube API JS fails to load, the rest of the JS should still run
Add retries when encountering DatabaseError when updating InstructorTask.
Merge pull request #1585 from edx/brian/retry-email-after-dbtimeout

Add retries when encountering DatabaseError when updating InstructorTask.